Today is June 13th (the same day as the film takes place).

Camp counselors Jack and Marcie are making love in a cabin during a rain storm

Lightening flashes and we see that in the bunk bed above their own, Ned is now dead:

Meanwhile Marcie has to pee so she leaves Jack alone in the lower bunk as she flees into the rainstorm clad only in a shirt and underwear, in search of a washroom. As Jack lights a cigarette a drop of blood from Ned’s corpse falls on his head. Before he has a chance to get up and investigate, the killer (who was under the bed the whole time Jack and Marcie were making love) panics and stabs him with an arrow from under the bed. Perhaps the most creative death scene in the history of horror:

Meanwhile Marcie is still peeing so the killer crawls out from under the bed towards the washrooms. Marcie hears someone has entered the washroom but when she can’t find anyone in either change room, she convinces herself “must be my imagination”.

But as soon as she says that we see the shadow of a huge axe rising on the wall behind her. She turns around and screams as the axe come flying into her face.