diff --git a/core/interpreter_test.cc b/core/interpreter_test.cc
index 25bf758a8..dc8b0ad2d 100644
--- a/core/interpreter_test.cc
+++ b/core/interpreter_test.cc
@@ -157,6 +157,18 @@ TEST_F(InterpreterTest, Basic) {
   }
 }
 
+TEST_F(InterpreterTest, UnknownFunc) {
+  string_view code(R"(
+    function foo(n)
+      return myunknownfunc(1, n)
+    end)");
+
+  CHECK_EQ(0, luaL_loadbuffer(lua(), code.data(), code.size(), "code1"));
+  CHECK_EQ(0, lua_pcall(lua(), 0, 0, 0));
+  int type = lua_getglobal(lua(), "myunknownfunc");
+  ASSERT_EQ(LUA_TNIL, type);
+}
+
 TEST_F(InterpreterTest, Stack) {
   RunInline(R"(
 local x = {}
diff --git a/server/command_registry.cc b/server/command_registry.cc
index 2f0ac6978..1029ac819 100644
--- a/server/command_registry.cc
+++ b/server/command_registry.cc
@@ -33,6 +33,7 @@ CommandRegistry::CommandRegistry() {
   CommandId cd("COMMAND", CO::RANDOM | CO::LOADING, 0, 0, 0, 0);
 
   cd.SetHandler([this](const auto& args, auto* cntx) { return Command(args, cntx); });
+
   const char* nm = cd.name();
   cmd_map_.emplace(nm, std::move(cd));
 }
@@ -70,6 +71,38 @@ CommandRegistry& CommandRegistry::operator<<(CommandId cmd) {
   return *this;
 }
 
+KeyIndex DetermineKeys(const CommandId* cid, const CmdArgList& args) {
+  DCHECK_EQ(0u, cid->opt_mask() & CO::GLOBAL_TRANS);
+
+  KeyIndex key_index;
+
+  if (cid->first_key_pos() > 0) {
+    key_index.start = cid->first_key_pos();
+    int last = cid->last_key_pos();
+    key_index.end = last > 0 ? last + 1 : (int(args.size()) + 1 + last);
+    key_index.step = cid->key_arg_step();
+
+    return key_index;
+  }
+
+  string_view name{cid->name()};
+  if (name == "EVAL" || name == "EVALSHA") {
+    DCHECK_GE(args.size(), 3u);
+    uint32_t num_keys;
+
+    CHECK(absl::SimpleAtoi(ArgS(args, 2), &num_keys));
+    key_index.start = 3;
+    key_index.end = 3 + num_keys;
+    key_index.step = 1;
+
+    return key_index;
+  }
+
+  LOG(FATAL) << "TBD: Not supported";
+
+  return key_index;
+}
+
 namespace CO {
 
 const char* OptName(CO::CommandOpt fl) {
diff --git a/server/command_registry.h b/server/command_registry.h
index cf74eade4..1e29a2819 100644
--- a/server/command_registry.h
+++ b/server/command_registry.h
@@ -37,8 +37,13 @@ const char* OptName(CommandOpt fl);
 
 class CommandId {
  public:
-  using Handler = std::function<void(CmdArgList, ConnectionContext*)>;
-  using ArgValidator = std::function<bool(CmdArgList, ConnectionContext*)>;
+  using Handler =
+      fu2::function_base<true /*owns*/, true /*copyable*/, fu2::capacity_default,
+                         false /* non-throwing*/, false /* strong exceptions guarantees*/,
+                         void(CmdArgList, ConnectionContext*) const>;
+
+  using ArgValidator = fu2::function_base<true, true, fu2::capacity_default, false, false,
+                                          bool(CmdArgList, ConnectionContext*) const>;
 
   /**
    * @brief Construct a new Command Id object
@@ -152,4 +157,8 @@ class CommandRegistry {
   void Command(CmdArgList args, ConnectionContext* cntx);
 };
 
+
+// Given the command and the arguments determines the keys range (index).
+KeyIndex DetermineKeys(const CommandId* cid, const CmdArgList& args);
+
 }  // namespace dfly
diff --git a/server/common_types.h b/server/common_types.h
index d7019e29c..a4d076a22 100644
--- a/server/common_types.h
+++ b/server/common_types.h
@@ -43,6 +43,12 @@ struct KeyLockArgs {
   unsigned key_step;
 };
 
+// Describes key indices.
+struct KeyIndex {
+  unsigned start;
+  unsigned end;  // does not include this index (open limit).
+  unsigned step; // 1 for commands like mget. 2 for commands like mset.
+};
 
 struct ConnectionStats {
   uint32_t num_conns = 0;
diff --git a/server/conn_context.h b/server/conn_context.h
index 39e59cbe9..92e5a5e96 100644
--- a/server/conn_context.h
+++ b/server/conn_context.h
@@ -4,6 +4,8 @@
 
 #pragma once
 
+#include <absl/container/flat_hash_set.h>
+
 #include "server/common_types.h"
 #include "server/reply_builder.h"
 
@@ -50,6 +52,8 @@ struct ConnectionState {
   // Lua-script related data.
   struct Script {
     bool is_write = true;
+
+    absl::flat_hash_set<std::string_view> keys;
   };
   std::optional<Script> script_info;
 };
diff --git a/server/db_slice.cc b/server/db_slice.cc
index ada37e045..16555befc 100644
--- a/server/db_slice.cc
+++ b/server/db_slice.cc
@@ -335,6 +335,9 @@ bool DbSlice::Acquire(IntentLock::Mode mode, const KeyLockArgs& lock_args) {
 }
 
 void DbSlice::Release(IntentLock::Mode mode, const KeyLockArgs& lock_args) {
+  DCHECK(!lock_args.args.empty());
+
+  DVLOG(2) << "Release " << IntentLock::ModeName(mode) << " for " << lock_args.args[0];
   if (lock_args.args.size() == 1) {
     Release(mode, lock_args.db_index, lock_args.args.front(), 1);
   } else {
@@ -351,7 +354,7 @@ void DbSlice::Release(IntentLock::Mode mode, const KeyLockArgs& lock_args) {
         }
       }
     }
-    DVLOG(1) << "Release " << IntentLock::ModeName(mode) << " for " << lock_args.args[0];
+
   }
 }
 
diff --git a/server/dragonfly_test.cc b/server/dragonfly_test.cc
index c3fe58b87..e2ac59d02 100644
--- a/server/dragonfly_test.cc
+++ b/server/dragonfly_test.cc
@@ -221,8 +221,22 @@ TEST_F(DflyEngineTest, Eval) {
   resp = Run({"incrby", "foo", "42"});
   EXPECT_THAT(resp[0], IntArg(42));
 
-  // resp = Run({"eval", "return redis.call('get', 'foo')", "0"});
-  // EXPECT_THAT(resp[0], StrArg("42"));
+  resp = Run({"eval", "return redis.call('get', 'foo')", "0"});
+  EXPECT_THAT(resp[0], ErrArg("undeclared"));
+
+  resp = Run({"eval", "return redis.call('get', 'foo')", "1", "bar"});
+  EXPECT_THAT(resp[0], ErrArg("undeclared"));
+
+  ASSERT_FALSE(service_->IsLocked(0, "foo"));
+
+  resp = Run({"eval", "return redis.call('get', 'foo')", "1", "foo"});
+  EXPECT_THAT(resp[0], StrArg("42"));
+
+  resp = Run({"eval", "return redis.call('get', KEYS[1])", "1", "foo"});
+  EXPECT_THAT(resp[0], StrArg("42"));
+
+  ASSERT_FALSE(service_->IsLocked(0, "foo"));
+  ASSERT_FALSE(service_->IsShardSetLocked());
 }
 
 TEST_F(DflyEngineTest, EvalSha) {
diff --git a/server/main_service.cc b/server/main_service.cc
index f43741b59..dc4c3bbd5 100644
--- a/server/main_service.cc
+++ b/server/main_service.cc
@@ -430,7 +430,18 @@ void Service::DispatchCommand(CmdArgList args, ConnectionContext* cntx) {
   // Create command transaction
   intrusive_ptr<Transaction> dist_trans;
 
-  if (!under_script) {
+  if (under_script) {
+    DCHECK(cntx->transaction);
+    KeyIndex key_index = DetermineKeys(cid, args);
+    for (unsigned i = key_index.start; i < key_index.end; ++i) {
+      string_view key = ArgS(args, i);
+      if (!cntx->conn_state.script_info->keys.contains(key)) {
+        return (*cntx)->SendError("script tried accessing undeclared key");
+      }
+    }
+    cntx->transaction->SetExecCmd(cid);
+    cntx->transaction->InitByArgs(cntx->conn_state.db_index, args);
+  } else {
     DCHECK(cntx->transaction == nullptr);
 
     if (IsTransactional(cid)) {
@@ -545,6 +556,7 @@ void Service::Multi(CmdArgList args, ConnectionContext* cntx) {
 }
 
 void Service::CallFromScript(CmdArgList args, ObjectExplorer* reply, ConnectionContext* cntx) {
+  DCHECK(cntx->transaction);
   InterpreterReplier replier(reply);
   ReplyBuilderInterface* orig = cntx->Inject(&replier);
 
@@ -647,6 +659,13 @@ void Service::EvalInternal(const EvalArgs& eval_args, Interpreter* interpreter,
   // and checking whether all invocations consist of RO commands.
   // we can do it once during script insertion into script mgr.
   cntx->conn_state.script_info.emplace();
+  for (size_t i = 0; i < eval_args.keys.size(); ++i) {
+    cntx->conn_state.script_info->keys.insert(ArgS(eval_args.keys, i));
+  }
+  DCHECK(cntx->transaction);
+
+  if (!eval_args.keys.empty())
+    cntx->transaction->Schedule();
 
   auto lk = interpreter->Lock();
 
@@ -659,6 +678,10 @@ void Service::EvalInternal(const EvalArgs& eval_args, Interpreter* interpreter,
 
   cntx->conn_state.script_info.reset();  // reset script_info
 
+  // Conclude the transaction.
+  if (!eval_args.keys.empty())
+    cntx->transaction->UnlockMulti();
+
   if (result == Interpreter::RUN_ERR) {
     string resp = absl::StrCat("Error running script (call to ", eval_args.sha, "): ", error);
     return (*cntx)->SendError(resp);
diff --git a/server/transaction.cc b/server/transaction.cc
index a6ba421a4..9af70c415 100644
--- a/server/transaction.cc
+++ b/server/transaction.cc
@@ -24,42 +24,6 @@ std::atomic_uint64_t op_seq{1};
 
 [[maybe_unused]] constexpr size_t kTransSize = sizeof(Transaction);
 
-struct KeyIndex {
-  unsigned start;
-  unsigned end;  // not including
-  unsigned step;
-};
-
-KeyIndex DetermineKeys(const CommandId* cid, const CmdArgList& args) {
-  DCHECK_EQ(0u, cid->opt_mask() & CO::GLOBAL_TRANS);
-
-  KeyIndex key_index;
-
-  if (cid->first_key_pos() > 0) {
-    key_index.start = cid->first_key_pos();
-    int last = cid->last_key_pos();
-    key_index.end = last > 0 ? last + 1 : (int(args.size()) + 1 + last);
-    key_index.step = cid->key_arg_step();
-
-    return key_index;
-  }
-
-  string_view name{cid->name()};
-  if (name == "EVAL" || name == "EVALSHA") {
-    DCHECK_GE(args.size(), 3u);
-    uint32_t num_keys;
-
-    CHECK(absl::SimpleAtoi(ArgS(args, 2), &num_keys));
-    key_index.start = 3;
-    key_index.end = 3 + num_keys;
-    key_index.step = 1;
-
-    return key_index;
-  }
-  LOG(FATAL) << "Not supported";
-
-  return key_index;
-}
 
 }  // namespace
 
@@ -130,7 +94,7 @@ OpResult<Transaction::FindFirstResult> Transaction::FindFirstProcessor::Process(
 }
 
 IntentLock::Mode Transaction::Mode() const {
-  return (trans_options_ & CO::READONLY) ? IntentLock::SHARED : IntentLock::EXCLUSIVE;
+  return (cid_->opt_mask() & CO::READONLY) ? IntentLock::SHARED : IntentLock::EXCLUSIVE;
 }
 
 /**
@@ -141,10 +105,15 @@ IntentLock::Mode Transaction::Mode() const {
  * @param cs
  */
 Transaction::Transaction(const CommandId* cid, EngineShardSet* ess) : cid_(cid), ess_(ess) {
-  if (strcmp(cid_->name(), "EXEC") == 0) {
+  string_view cmd_name(cid_->name());
+  if (cmd_name == "EXEC" || cmd_name == "EVAL" || cmd_name == "EVALSHA") {
     multi_.reset(new Multi);
+    multi_->multi_opts = cid->opt_mask();
+
+    if (cmd_name == "EVAL" || cmd_name == "EVALSHA") {
+      multi_->incremental = false;  // we lock all the keys at once.
+    }
   }
-  trans_options_ = cid_->opt_mask();
 }
 
 Transaction::~Transaction() {
@@ -185,22 +154,19 @@ void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
 
   KeyIndex key_index = DetermineKeys(cid_, args);
 
-  if (key_index.start == args.size()) {
+  if (key_index.start == args.size()) {  // eval with 0 keys.
     CHECK(absl::StartsWith(cid_->name(), "EVAL"));
     return;
   }
 
   DCHECK_LT(key_index.start, args.size());
+  DCHECK_GT(key_index.start, 0u);
 
-  bool single_key = key_index.start > 0 && !cid_->is_multi_key();
-  if (!multi_ && single_key) {
+  bool incremental_locking = multi_ && multi_->incremental;
+  bool single_key = !multi_ && (key_index.start + key_index.step) >= key_index.end;
+
+  if (single_key) {
     shard_data_.resize(1);  // Single key optimization
-  } else {
-    // Our shard_data is not sparse, so we must allocate for all threads :(
-    shard_data_.resize(ess_->size());
-  }
-
-  if (!multi_ && single_key) {  // Single key optimization.
     auto key = ArgS(args, key_index.start);
     args_.push_back(key);
 
@@ -210,10 +176,12 @@ void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
     return;
   }
 
+  // Our shard_data is not sparse, so we must allocate for all threads :(
+  shard_data_.resize(ess_->size());
   CHECK(key_index.step == 1 || key_index.step == 2);
   DCHECK(key_index.step == 1 || (args.size() % 2) == 1);
 
-  // Reuse thread-local temporary storage. Since this code is non-preemptive we can use it here.
+  // Reuse thread-local temporary storage. Since this code is atomic we can use it here.
   auto& shard_index = tmp_space.shard_cache;
   shard_index.resize(shard_data_.size());
   for (auto& v : shard_index) {
@@ -223,10 +191,12 @@ void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
   // TODO: to determine correctly locking mode for transactions, scripts
   // and regular commands.
   IntentLock::Mode mode = IntentLock::EXCLUSIVE;
+  bool should_record_locks = false;
   if (multi_) {
     mode = Mode();
     tmp_space.uniq_keys.clear();
     DCHECK_LT(int(mode), 2);
+    should_record_locks = incremental_locking || !multi_->locks_recorded;
   }
 
   for (unsigned i = key_index.start; i < key_index.end; ++i) {
@@ -235,7 +205,7 @@ void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
     shard_index[sid].args.push_back(key);
     shard_index[sid].original_index.push_back(i - 1);
 
-    if (multi_ && tmp_space.uniq_keys.insert(key).second) {
+    if (should_record_locks && tmp_space.uniq_keys.insert(key).second) {
       multi_->locks[key].cnt[int(mode)]++;
     };
 
@@ -247,6 +217,10 @@ void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
     }
   }
 
+  if (multi_) {
+    multi_->locks_recorded = true;
+  }
+
   args_.resize(key_index.end - key_index.start);
   reverse_index_.resize(args_.size());
 
@@ -263,7 +237,14 @@ void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
 
     sd.arg_count = si.args.size();
     sd.arg_start = next_arg - args_.begin();
-    sd.local_mask = 0;
+
+    // We reset the local_mask for incremental locking to allow locking of arguments
+    // for each operation within the same transaction. For instant locking we lock at
+    // the beginning all the keys so we must preserve the mask to avoid double locking.
+    if (incremental_locking) {
+      sd.local_mask = 0;
+    }
+
     if (!sd.arg_count)
       continue;
 
@@ -297,7 +278,8 @@ void Transaction::InitByArgs(DbIndex index, CmdArgList args) {
 
   // Validation.
   for (const auto& sd : shard_data_) {
-    DCHECK_EQ(sd.local_mask, 0u);
+    // sd.local_mask may be non-zero for multi transactions with instant locking.
+    // Specifically EVALs may maintain state between calls.
     DCHECK_EQ(0, sd.local_mask & ARMED);
     if (!multi_) {
       DCHECK_EQ(TxQueue::kEnd, sd.pq_pos);
@@ -309,13 +291,17 @@ void Transaction::SetExecCmd(const CommandId* cid) {
   DCHECK(multi_);
   DCHECK(!cb_);
 
+  // The order is important, we are Schedule() for multi transaction before overriding cid_.
+  // TODO: The flow is ugly. I should introduce a proper interface for Multi transactions
+  // like SetupMulti/TurndownMulti. We already have UnlockMulti that should be part of
+  // TurndownMulti.
+
   if (txid_ == 0) {
     Schedule();
   }
 
   unique_shard_cnt_ = 0;
   cid_ = cid;
-  trans_options_ = cid->opt_mask();
   cb_ = nullptr;
 }
 
@@ -344,6 +330,7 @@ bool Transaction::RunInShard(EngineShard* shard) {
   DCHECK_EQ(sd.local_mask & (SUSPENDED_Q | EXPIRED_Q), 0);
 
   bool awaked_prerun = (sd.local_mask & AWAKED_Q) != 0;
+  bool incremental_lock = multi_ && multi_->incremental;
 
   // For multi we unlock transaction (i.e. its keys) in UnlockMulti() call.
   // Therefore we differentiate between concluding, which says that this specific
@@ -354,8 +341,8 @@ bool Transaction::RunInShard(EngineShard* shard) {
   IntentLock::Mode mode = Mode();
 
   // We make sure that we lock exactly once for each (multi-hop) transaction inside
-  // multi-transactions.
-  if (multi_ && ((sd.local_mask & KEYLOCK_ACQUIRED) == 0)) {
+  // transactions that lock incrementally.
+  if (incremental_lock && ((sd.local_mask & KEYLOCK_ACQUIRED) == 0)) {
     DCHECK(!awaked_prerun);  // we should not have blocking transaction inside multi block.
 
     sd.local_mask |= KEYLOCK_ACQUIRED;
@@ -458,6 +445,11 @@ void Transaction::ScheduleInternal() {
 
   uint32_t num_shards;
   std::function<bool(uint32_t)> is_active;
+
+  // TODO: For multi-transactions we should be able to deduce mode() at run-time based
+  // on the context. For regular multi-transactions we can actually inspect all commands.
+  // For eval-like transactions - we can decided based on the command flavor (EVAL/EVALRO) or
+  // auto-tune based on the static analysis (by identifying commands with hardcoded command names).
   IntentLock::Mode mode = Mode();
 
   if (span_all) {
@@ -534,6 +526,10 @@ OpStatus Transaction::ScheduleSingleHop(RunnableType cb) {
   // single hop -> concluding.
   coordinator_state_ |= (COORD_EXEC | COORD_EXEC_CONCLUDING);
 
+  if (!multi_) {   // for non-multi transactions we schedule exactly once.
+    DCHECK_EQ(0, coordinator_state_ & COORD_SCHED);
+  }
+
   bool schedule_fast = (unique_shard_cnt_ == 1) && !IsGlobal() && !multi_;
   if (schedule_fast) {  // Single shard (local) optimization.
     // We never resize shard_data because that would affect MULTI transaction correctness.
@@ -598,7 +594,10 @@ void Transaction::UnlockMulti() {
   auto cb = [&] {
     EngineShard* shard = EngineShard::tlocal();
 
-    shard->shard_lock()->Release(IntentLock::EXCLUSIVE);
+    if (multi_->multi_opts & CO::GLOBAL_TRANS) {
+      shard->shard_lock()->Release(IntentLock::EXCLUSIVE);
+    }
+
     ShardId sid = shard->shard_id();
     for (const auto& k_v : sharded_keys[sid]) {
       auto release = [&](IntentLock::Mode mode) {
@@ -606,6 +605,7 @@ void Transaction::UnlockMulti() {
           shard->db_slice().Release(mode, this->db_index_, k_v.first, k_v.second.cnt[mode]);
         }
       };
+
       release(IntentLock::SHARED);
       release(IntentLock::EXCLUSIVE);
     }
@@ -1102,7 +1102,7 @@ inline uint32_t Transaction::DecreaseRunCnt() {
 }
 
 bool Transaction::IsGlobal() const {
-  return (trans_options_ & CO::GLOBAL_TRANS) != 0;
+  return (cid_->opt_mask() & CO::GLOBAL_TRANS) != 0;
 }
 
 // Runs only in the shard thread.
diff --git a/server/transaction.h b/server/transaction.h
index 8a587e261..8cb083eba 100644
--- a/server/transaction.h
+++ b/server/transaction.h
@@ -127,8 +127,7 @@ class Transaction {
     return txid_;
   }
 
-  // TODO: for multi trans_options_ changes with every operation.
-  // Does it mean we lock every key differently during the same transaction?
+  // based on cid_->opt_mask.
   IntentLock::Mode Mode() const;
 
   const char* Name() const;
@@ -266,6 +265,10 @@ class Transaction {
 
   struct Multi {
     absl::flat_hash_map<std::string_view, LockCnt> locks;
+    uint32_t multi_opts = 0;  // options of the parent transaction.
+
+    bool incremental = true;
+    bool locks_recorded = false;
   };
 
   util::fibers_ext::EventCount blocking_ec_;  // used to wake blocking transactions.
@@ -298,8 +301,6 @@ class Transaction {
   // unique_shard_cnt_ and unique_shard_id_ is accessed only by coordinator thread.
   uint32_t unique_shard_cnt_{0};  // number of unique shards span by args_
 
-  uint32_t trans_options_ = 0;
-
   ShardId unique_shard_id_{kInvalidSid};
   DbIndex db_index_ = 0;
 
@@ -309,6 +310,7 @@ class Transaction {
   enum CoordinatorState : uint8_t {
     COORD_SCHED = 1,
     COORD_EXEC = 2,
+
     // We are running the last execution step in multi-hop operation.
     COORD_EXEC_CONCLUDING = 4,
     COORD_BLOCKED = 8,