(Based off of a fan game)
(A) get's kidnapped by someone on their way back to school for (reason), plain and simple, and everyone is scared that they're going to die. So their classmates start up their own investigation. (B) is especially fearful for what might happen to (A) because they are close (romantically or amicably), and, they put on something of (A)'s, like a hat, or a jacket, just to make it feel like they're still around. But, they close their eyes and suddenly they're in a different room, the one where (a)'s currently held.
Whatever happens next is up to you.