Bobby Newkirk is a dick, and by dick, I mean the type of guy who goes through every girl in school and gets bored fast. After trapping one girl, Ronnie, in her locker and kissing her, he tells her that he might call her again. On his way to band practice, he sees another girl, Kimmy, who he stood up the night before for a “better” date.
While at practice, he sees twins Bree and Samantha. He always thought about asking them out before but he couldn't decide between the two. Bobby makes a joke about dating them both in one weekend and decides that he should try it. Arnie's girlfriend Melanie warns him about playing girls. She dated him for three months before dumping him for cheating on her.
Bobby sees Bree after school and asks her to come see their band play that Friday. He also suggests she become their lead singer, but she says it sounds more like something Samantha would like. Later that night, he calls Samantha and asks her to join the band, and she shoots him down. He asks her on a date and somehow convinces her that she should keep it a secret from her sister.
Bree is mellow and quiet, doesn't really enjoy dancing with him, and seems like a shy girl. After leaving the dance club, they go for a drive in his car and she grabs him and kisses him. The next day, he meets Samantha at the mall and they decide to window shop instead of seeing a movie. Samantha wanders into a earring shop, tries on a few different pairs, and then spices things up by running out with them on her ears.
They run through the mall and get caught by a security guard who just warns them about running in the mall because of the slippery floors. She demands his keys and takes him on a wild ride through town, driving way above the speed limit. She takes him up to the big makeout spot and they kiss for hours.
Melanie warns him again about messing with the twins, but he still doesn't listen. She heard through the grapevine that Bree almost caught him with her sister who escaped by sneaking out his back door. Bree comes over to his house, upset over something. He thinks that she knows the truth, but she's really just upset because Samantha is dating someone and won't tell her who, and her sister usually tells her everything. Samantha then calls to warn him about her twin. She makes it clear that she wants him to tell her sister because she's tired of sharing him, and she warns him that when her twin breaks, things are bad.
So, he obviously decides to keep dating both girls at once. He meets Samantha at the mall, and she tells him that it's his turn to steal something. She wants a silver charm bracelet, and she convinces him that it's easy. He lifts up the case and an alarm goes off, but he still gets away with the bracelet. Bree sees them in the mall, and they convince her that they just ran into each other. He briefly notices that Samantha looks scared of her twin before wondering if he can convince them to go out on a double date, but they leave together.
When he gets outside, he notices that his car looks funny. It turns out that someone slashed his two front tires, and he sees a familiar smiley face nearby. Melanie pulls up, acts like she was just passing by, and offers him a ride home. He talks to Samantha about it, wondering if Bree did it.
Samantha comes up to him in school, saying that she wants him to see her science project. She drags him into the lab and they make out a little. He shows her his monkeys Wayne and Garth, and she decides to show him how to tell the twins apart. She has a tiny blue butterfly tattoo on her shoulder. She also shows him her project, which uses cannibal ants.
The band gets the chance to play for the whole school, and Bobby acts like he's the star. He goes to play a chord and he feels a big shock and passes out. Someone plugged his guitar into the wrong spot and he got knocked out. Melanie once again warns him about dating the Wade twins, but he thinks that she's just jealous and wants another shot with him.
He and Samantha later go out on a date, and she's acting as wild as usual. Her shirt slips down and she doesn't have a tattoo. He accuses her of being Bree and tricking him, but she tells him that she's crazy and her parents would kill her if she got a tattoo. She then pouts and tells him to take her home because he's no longer in the mood.
While talking to Samantha on the phone that night, Bree walks in, but he lies and says it was Arnie. They snuggle a little, and he thinks about how much Samantha wants him to dump her twin. When he goes back to school, he notices a weird smell near his locker. He pulls open the door and finds a bloody monkey head looking back at him.
You don't need to call PETA on Stine though, because it's just a plastic monkey head. He's still a little freaked out when he goes out with Samantha. She takes him to a secluded cabin in the middle of the woods and announces that she has a new plan: she thinks that they should kill Bree. She keeps pushing the issue until he agrees, but he really plans on warning her. He also notices that she doesn't have a tattoo and she says she never had one.
Bobby gets Bree alone and tells her what happened, which upsets her. She tells him that they aren't twins, they are actually triplets. Their sister Jennilynn was always jealous of them. When they were kids, she locked them in their room and set fire to the house. She's been in a mental institution, and when she got out, they sent her to live with relatives. Bree tells him that Jennilynn has a butterfly tattoo on her shoulder and rushes home to warn her twin.
Samantha calls and tells him that Bree lost her marbles. She only makes up stories about a triplet when things are bad, and she will need to tell her parents what happened. The next time he sees her, he begs to see her tattoo and she thinks he's crazy because she never had one.
This all leads up to one of the twins showing up at his home. She says that she's Samantha and he sees the tattoo, which she says that she always had. She takes him to the cabin and asks if he's ready to kill her sister. She goes a little crazy and knocks him out, and he wakes up tied to a chair. The twin says that she's Jennilynn and threatens him. She pours honey all over his body, burns his pants in the fireplace, and releases the cannibal ants.
Bobby immediately starts screaming because it feels like thousands of insects biting him all over his body. He tips the chair over, and she runs out of the house. He manages to get the knots loose and rushes outside where he finds Melanie. She tells him that someone stole the twins' car and that they think it was Jennilynn. They decide to rush back to their house and warn them before it's too late.
He's covered in honey with grass stuck all over him and no pants, but he still bursts into their house. He notices a bunch of girls who look like most of his exes sitting around the room. Mr. Wade comes in and when Bobby rambles about a triplet, he thinks that he's drunk. He tells them that they don't have a cabin, they are only twins, and he should go home. He brings up the tattoo, and both girls show their shoulders are bare. Everyone laughs at him and he walks home defeated.
A few days later, Bobby is back at school. Arnie sold his drums and quit the band, and their other bandmate joined another group. He sees the twins walking down the hallway, and Bree hands him an envelope. He opens it up and finds a note telling him that they knew his plan from the beginning because twins don't keep secrets. In the bottom of the envelope is a temporary blue butterfly tattoo.