A grisly attack has left five people seriously injured. Investigators have only hair, blood, a fingerprint and grainy CCTV footage to go on.
Using sophisticated forensic techniques, they must solve the gruesome mystery before someone else is hurt.
But there's a twist - the victims are not real people, but teddy bears. The investigators are 13-year-olds and the techniques can be found in an ordinary science classroom.
Like an episode of CSI: Papakura, the Year 9 class at Rosehill College, in South Auckland, must channel all their investigative powers to eliminate the suspects in crime, set by science teacher Alice Nash.
"For the first lesson I got the police tape, and basically bordered off [the doors] so they had to climb through the police tape to get into the lab.
"Other classes were coming past thinking something had actually happened, that was great for impact."
Once inside, they discovered the mock crime scene, with chalk outlines and fake blood. The students, dressed in forensic gloves, goggles, booties and overalls, then had to secure the scene and collect evidence.
"CSI is really fun, we've got to wear all the gear and learn how real CSI detectives work," Taylor Parker, 13, right, said. "It's better than just sitting and writing."
His favourite part was "getting to wear the gear" and trying to solve the crime, he said.
"We had three suspects, two of them had dogs [and one owned a horse], but we eliminated the first suspect as we looked at the hair at the crime scene and it was dog hair," Taylor explained.
"Then we looked at the lollies found at the crime scene and it was a jelly bean, eliminating the second person [who prefers marshmallows], but we can't fully eliminate the second person yet as they also have a dog. So we're fingerprinting now."
The class had helped with his understanding of science, he said, and had sparked an interest in becoming a crime scene investigator.
Jacob Ford, 13, agreed, saying: "I think it's really interesting because you learn lots of cool things."
So far they've examined mock security footage, hair samples and used chromatography to identify the type of lolly left at the crime scene.
"They're learning and they don't realise they're learning sometimes," said Nash.
"So instead of me just standing at the front telling them it, they're actually working it out. They're learning in context and finding it themselves."
The unit takes them through the practical skills they'll need for science lessons for the rest of their school years, she said, but in a more interesting and engaging way.
"So far they're enjoying it," she said. "I think engagement has definitely gone up."
And it's not just the Year 9s who are gripped by the mystery - other classes are hooked on the whodunnit too.
"They come in and they're like, 'tell us, Miss, who did it?'."
But she remained tight-lipped: "You have to work it out for yourself."