Title: Seven Days in November by Brandon D. Ray
Pairing: Gen, minor Bill/Tara
Author on LJ: n/a
Author Website: Brandon's Gossamer pageWhy this must be read: This story is part of Brandon's campaign to "salvage Bill Scully, jr's poor, pathetic soul", and he does a damn good job of it. He's still recognizably the overprotective, bully-ish older brother we meet in the series, but Brandon writes him in a much more sympathetic light than many other authors I've read.
The crossover aspect is the plot of the book (also a movie) "Seven Days in May" transposed in the X-Files universe. It's not a complete reproduction of the plot, since the main character of the book is more peripheral here and the story is told from Bill's perspective. The crossover leans more towards the X-Files universe; you don't have to read or see "Seven Days in May" to understand what's going on--I haven't. And I might have passed this story by, just because I didn't know the other fandom--but I had faith in Brandon's ability to suck me into the story and have everything make sense, and I wasn't disappointed.
Seven Days in November