In the rafters for a good sniping point
From Create Your Own Story
You climb up to the rafters of the fort and look down the sights of your scope. You don't see any BLU team members but, to your alarm, you do see the bloodied body of a RED team Soldier. The Soldier that was talking to you must have been a spy. You call down to your other teammates and ask if they know where The Soldier went but no one knows. Then a loud explosion occurs in a nearby hallway and BLU HWG's come in with their Mini-gun's blazing. You see the Engineer go down in a bloody mess followed by The medic but then the Demo-Man's sticky bombs go off and both HWG's are turned into bloody puddles in an instant. You shoot a BLU team Medic that was running to the Intelligence room and it seems like the attack is over.
Until you see a BLU Pyro and a BLU Soldier cornering a RED Scout.
You're about to take aim at the Pyro but suddenly you hear the RED HWG shout "A SPY!" followed by a loud thump.
You know that a Spy always kills the person that reveals them but a GOOD Spy kills them quickly.
You can either save the RED Scout or kill the BLU spy now.
