They Promised Me the Gun Wasn't Loaded by James Alan Gardner - This is the sequel to All Those Explosions Were Someone Else's Fault, which I haven't read yet but which sounds hilarious.
Only days have passed since a freak accident granted four college students superhuman powers. Now Jools and her friends (who haven't even picked out a name for their superhero team yet) get caught up in the hunt for a Mad Genius's misplaced super-weapon.
But when Jools falls in with a modern-day Robin Hood and his band of super-powered Merry Men, she finds it hard to sort out the Good Guys from the Bad Guys-and to figure out which side she truly belongs on.
Especially since nobody knows exactly what the Gun does . . . .