Where Is Falx Carius?

[Ricebug]

I'm doing the March of the Dead quest. I'm toasting marshmallows here at Fort Frostmoth because I cannot, for the life of me, find this Captain Carius. Searched every room in the place except for the room that needs a key. Cannot find that key, either.

EDIT: Looking at the Skyrim Item List, there is a key but it says Dawnguard DLC Code + 01F4B4. Is this a mod?

EDIT: I cheated my way past the door and found the Captain. Found the key on his corpse. How is a person supposed to unlock a door with a key that's on the OTHER side of same door???

[Perplex]

Because you go under the complex from one building to another via tunnels.

[MysticMalevolence]

You went through the exit door. There's a path through one of the other buildings to him.

[Ricebug]

Yeah, I accidentally stumbled upon it after posting. Always happens.