diff --git a/src/ims/directory/clubhouse_db/_directory.py b/src/ims/directory/clubhouse_db/_directory.py
index 0d3eea0ff..979e44dce 100644
--- a/src/ims/directory/clubhouse_db/_directory.py
+++ b/src/ims/directory/clubhouse_db/_directory.py
@@ -27,7 +27,7 @@
 from ims.directory import IMSDirectory, IMSGroupID, IMSTeamID, IMSUser, userFromRanger
 from ims.model import Ranger
 
-from ._dms import DutyManagementSystem
+from ._dms import DutyManagementSystem, Position, Team
 
 
 __all__ = ()
@@ -48,22 +48,37 @@ async def personnel(self) -> Iterable[Ranger]:
 
     async def lookupUser(self, searchTerm: str) -> IMSUser | None:
         dms = self._dms
+        # call out to a more easily testable static method
+        return DMSDirectory._lookupUser(
+            searchTerm,
+            tuple(await dms.personnel()),
+            tuple(await dms.positions()),
+            tuple(await dms.teams()),
+        )
 
-        # FIXME: a hash would be better (eg. rangersByHandle)
-        rangers = tuple(await dms.personnel())
-
-        for ranger in rangers:
-            if ranger.handle == searchTerm:
+    @staticmethod
+    def _lookupUser(
+        searchTerm: str,
+        rangers: tuple[Ranger, ...],
+        positions: tuple[Position, ...],
+        teams: tuple[Team, ...],
+    ) -> IMSUser | None:
+        searchLower = searchTerm.lower()
+
+        ranger = None
+
+        for r in rangers:
+            if r.handle.lower() == searchLower:
+                ranger = r
+            for email in r.email:
+                if email.lower() == searchLower:
+                    ranger = r
+            if ranger is not None:
                 break
         else:
-            for ranger in rangers:
-                if searchTerm in ranger.email:
-                    break
-            else:
-                return None
-
-        positions = tuple(await dms.positions())
-        teams = tuple(await dms.teams())
+            return None
+
+        assert ranger is not None
 
         groups = tuple(
             IMSGroupID(position.name)
diff --git a/src/ims/directory/clubhouse_db/test/test_directory.py b/src/ims/directory/clubhouse_db/test/test_directory.py
index c331c8b12..4af46f927 100644
--- a/src/ims/directory/clubhouse_db/test/test_directory.py
+++ b/src/ims/directory/clubhouse_db/test/test_directory.py
@@ -18,12 +18,52 @@
 Tests for L{ims.directory.clubhouse_db._directory}.
 """
 
+from ims.directory import IMSUser
+from ims.directory.clubhouse_db import DMSDirectory
+from ims.directory.clubhouse_db._dms import Position, Team
 from ims.ext.trial import TestCase
+from ims.model import Ranger, RangerStatus
 
 
 __all__ = ()
 
 
+def _ranger_alpha() -> Ranger:
+    return Ranger(
+        handle="Alpha",
+        status=RangerStatus.active,
+        email=frozenset(["alpha@example.com"]),
+        onsite=False,
+        directoryID=None,
+    )
+
+
+def _ranger_beta() -> Ranger:
+    return Ranger(
+        handle="Beta",
+        status=RangerStatus.active,
+        email=frozenset(["beta@example.com"]),
+        onsite=True,
+        directoryID=None,
+    )
+
+
+def _position_delta() -> Position:
+    return Position(
+        positionID="ddd",
+        name="Delta",
+        members={_ranger_alpha()},
+    )
+
+
+def _team_upsilon() -> Team:
+    return Team(
+        teamID="uuu",
+        name="Upsilon",
+        members={_ranger_beta()},
+    )
+
+
 class DMSDirectoryTests(TestCase):
     """
     Tests for :class:`DMSDirectory`
@@ -35,6 +75,39 @@ def test_personnel(self) -> None:
     test_personnel.todo = "unimplemented"  # type: ignore[attr-defined]
 
     def test_lookupUser(self) -> None:
-        raise NotImplementedError()
+        def lookup(search: str) -> IMSUser | None:
+            return DMSDirectory._lookupUser(
+                search,
+                (_ranger_alpha(), _ranger_beta()),
+                (_position_delta(),),
+                (_team_upsilon(),),
+            )
+
+        # Case-insensitive matching against handles and email addresses
+        self.assertIsNotNone(lookup("alpha"))
+        self.assertIsNotNone(lookup("Alpha"))
+        self.assertIsNotNone(lookup("beta@example.com"))
+        self.assertIsNotNone(lookup("ALPHA@exAMple.com"))
+
+        # Failures to match against handle or email address
+        self.assertIsNone(lookup("NotARanger@example.com"))
+        self.assertIsNone(lookup("BetaWithSuffix"))
 
-    test_lookupUser.todo = "unimplemented"  # type: ignore[attr-defined]
+        # Now check the various fields that come back, including
+        # positions and teams set up at the top of this test file.
+        alpha = lookup("alpha")
+        beta = lookup("BETA@EXAMPLE.COM")
+        self.assertIsNotNone(alpha)
+        # to appease mypy
+        assert alpha is not None
+        self.assertEqual(alpha.uid, "Alpha")
+        self.assertEqual(alpha.shortNames, ("Alpha",))
+        self.assertEqual(alpha.onsite, False)
+        self.assertEqual(alpha.groups, ("Delta",))
+        self.assertEqual(alpha.teams, ())
+        self.assertIsNotNone(beta)
+        # to appease mypy
+        assert beta is not None
+        self.assertEqual(beta.onsite, True)
+        self.assertEqual(beta.groups, ())
+        self.assertEqual(beta.teams, ("Upsilon",))