diff --git a/hy_memory/agent/episode_summary.py b/hy_memory/agent/episode_summary.py
index 377350e..d48cd08 100644
--- a/hy_memory/agent/episode_summary.py
+++ b/hy_memory/agent/episode_summary.py
@@ -39,6 +39,7 @@ import logging
 import hashlib
 import json
 import re
+from datetime import datetime
 from typing import Any, Dict, List, Optional
 import uuid
 
@@ -252,6 +253,17 @@ def _series_episode_id(
     return str(uuid.uuid5(uuid.NAMESPACE_URL, "hy-memory:series-episode:" + raw))
 
 
+def _series_memory_at(times: List[int]) -> Optional[datetime]:
+    """Earliest member timestamp as the same local wall clock it came from.
+
+    ``_node_timestamp`` produces ``datetime.timestamp()`` values. Reading them
+    back with ``utcfromtimestamp`` turns them into a naive *UTC* datetime, which
+    the vector payload later re-interprets as local time and shifts by the
+    machine's UTC offset.
+    """
+    return datetime.fromtimestamp(min(times)) if times else None
+
+
 def _node_timestamp(node: Any) -> Optional[int]:
     value = getattr(node, "memory_at", None) or getattr(node, "gmt_created", None)
     if value is None:
@@ -974,8 +986,6 @@ async def finalize_series_episode_containers(
     Stored text is only a title plus a structural intro. Exact L2 bodies remain in
     their canonical nodes and are referenced by ID from dated timeline segments.
     """
-    from datetime import datetime
-
     from ..models.memory import MemoryLayer, MemoryNode, MemoryStatus, SourceType
     from ..pipelines._retrieval.session_episode import (
         add_parent_episode_membership,
@@ -1061,7 +1071,7 @@ async def finalize_series_episode_containers(
             segment["memory_at"] for segment in plan["timeline"]
             if segment.get("memory_at") is not None
         ]
-        memory_at = datetime.utcfromtimestamp(min(times)) if times else None
+        memory_at = _series_memory_at(times)
         content = f"{plan['title']}. {plan['intro']}".strip()
         series = MemoryNode(
             node_id=series_id, user_id=user_id,
diff --git a/tests/test_episode.py b/tests/test_episode.py
index 943e213..5dbebc0 100644
--- a/tests/test_episode.py
+++ b/tests/test_episode.py
@@ -710,3 +710,20 @@ class TestInstrumentation:
         assert logged[1]["count"] == 5, "累计条数要落下来"
         assert logged[2]["reused"] is False
         assert all(r["gap"] == 1800.0 for r in logged)
+
+
+def test_series_memory_at_round_trips_local_wall_clock(monkeypatch):
+    """Series timestamps must not shift by the machine's UTC offset."""
+    import time as _time
+
+    from hy_memory.agent.episode_summary import _series_memory_at
+
+    monkeypatch.setenv("TZ", "Asia/Shanghai")
+    _time.tzset()
+    try:
+        expected = datetime(2026, 1, 1, 12, 0)
+        assert _series_memory_at([int(expected.timestamp())]) == expected
+        assert _series_memory_at([]) is None
+    finally:
+        monkeypatch.delenv("TZ", raising=False)
+        _time.tzset()