How can I get Derkeethus back to Sky Haven Temple?

After completing the Blades quest I made Athis, Ghorbash the Iron Hand, and Derkeethus the new recruits for the Blades. (Derkeethus was the first one I recruited, if that information helps with anything.) Ghorbash and Athis live normally in Sky Haven Temple with Delphine and Esbern, but Derkeethus is not showing up. After I recruited him he just went back to Dark Water Crossing. When I go to Dark Water Crossing he goes to the temple like he is supposed to, but when I return to the Temple he leaves and goes to Dark Water Crossing! I'd like to fight with my three favorite followers, but he isn't showing up at the temple or at the battles when we fight the dragons Ebern sends us to. I've tried everything I can think of to get him there but nothing is working. Help!

Solution 1:

This is actually a known bug for Derkeethus. He has quite a few of them; more than many followers in Skyrim, and that's saying something. I always felt like he was the follower that BethSoft let the intern script.

In addition to failing to participate in his Bladely duties unless he is your active follower, other issues include:

• If you marry him (...how does that work if you aren't Argonian...), he may randomly sprint out of the wedding mid-ceremony and bolt for DarkWater Crossing
• He will sometimes refuse to use a better bow than his hunting bow. You can even rob him of it and he'll wear it on his back.
• If you marry him and ask him to move in, because you don't want to live in a tent, he will get lost partway there and become homeless forever, wandering Skyrim unless he's following you.
• Some clothing items appear invisible on him
• He can forever get stuck in DarkWater Pass if you return there
• If at any point he is attacked when not your follower and put in "incapacitated" status (kneeling), he is very likely to get up and sprint back to Darkwater Crossing.
• He sometimes speaks in a Dunmer voice
• If you marry him AND he joins the Blades, he may at any point suddenly reset his entire inventory to his starting inventory
• He will sometimes say he's going to follow you when he gets out of a bed, then, you guessed it, run back to Darkwater Crossing.

Judging from the amount of times the darn lizard runs back to Darkwater Crossing, and how it overrides his other behaviors so much, it's pretty clear what happened. DK's script was causing problems with his quest and he kept wandering out of the cave before you could rescue him, so someone overcompensated by adding invasive scripting that makes him unreasonably homesick. I'm not sure if the Unofficial Patch on the Nexus has this in its fix list. I might recommend AFT, a follower mod for PC, which will let you directly modify his behavior and override his scripts.