April Fool's Day is a 1986 horror/comedy film released by Paramount Pictures. It was directed by Fred Walton, from the screenplay by Danilo Bach. The original music score was composed by Charles Bernstein. The film is marketed with the tagline "Don't let the joke be on you!"
It was filmed in British Columbia, Canada and has a largely Canadian cast.
Once on the island and in the mansion, it turns out Muffy has set up a ton of little jokes from the simple (whoopee cushions, dribble glasses, etc.) to the more complex and disturbing (an audiotape of a baby crying in someone's room, heroin paraphernalia in a guest's wardrobe, etc.) Through it all, the friends in general try to relax. They flirt. They share stories. Two of them hook up. Rob Ferris (Olandt) tells his girlfriend and fiancee Kit Graham (Steel) he wasn't accepted into medical school.
But then, Skip goes missing. Kit catches a glimpse of what looks like his dead body. Arch and Nan go missing. During a search, Nikki falls into the island's well and finds the severed heads of Skip and Arch. Worse, the phones are dead as well. There's no way to get off the island until Monday.
One after another, people keep vanishing or killed and their bodies found — by hanging, throat-slitting, and in one instance castration. Kit and Rob put together some clues, realizing that everyone's earlier assumption is wrong. The kinsman of the deckhand injured when they arrived is a red herring. Muffy, it turns out, has a violently insane twin sister, Buffy, who has escaped. In fact, the person they've been around since the first night isn't Muffy at all! They discover Muffy's severed head in the basement.
Buffy chases them with a butcher's knife, and the couple are separated. Kit flees from Buffy into the living room — where she finds everyone else there, alive and calmly waiting for her. It was all a joke, or more accurately, a dress rehearsal. Muffy hopes to turn the mansion into a resort offering a weekend of staged horror. She even had a friend who does special effects and make-up for Hollywood help. Each "victim" agreed to take part as things were explained to them.
Everyone has a huge laugh, and break out lots of bottles of champagne. Much later that night, a half-drunk Muffy goes to her room. She finds a wrapped present on her bed. Grinning, she unwraps it. It is the Jack-in-the-Box. Savoring the surprise, she turns the handle slowly. When "Jack" finally pops out, Nan — the shy, bookish girl who knew Muffy from acting class — emerges from behind her and slits her throat with a razor. Muffy screams. Then realizes she isn't really bleeding. She "got" her with a trick razor and stage blood only.
Jeff Rovin's novelization features the infamous ending in which Skip sneaks back onto the island after everyone has left to kill Muffy for her share of the family money, though he fails and winds up dead himself. This ending has never been released, but stills of it have surfaced.
A revised draft of the script included another version of the above-mentioned ending in which Skip sneaks back onto the island to slay Muffy. He springs out of a closet and slits her throat, and she at first panics but realizes it is all a joke when she sees her friends standing around. The script then states that Skip stays on the island to help Muffy with the bed and breakfast.