Somewhere a Clock is Ticking, by
parenthetical. 70K of Sam/Dean.
Summary: When Ben goes missing, Dean has to help, even if it means going in without Sam. By the time he stops to consider the consequences, it's already too late, and Sam's skating dangerously close to the edge in his determination to fix things.
I was lucky enough to beta read this one, and now I get to read it again. If you like Sam and Dean, then check it out.