Hundreds of pupils became Poirots and Miss Marples when they ditched their conventional lessons to solve a murder mystery at their school.
The young Inspector Morses from Canons High School in Edgware became detectives in an attempt to catch the killer of assistant headteacher, Mr Green.
Throughout the day classrooms were turned into forensic science labs for children to crack codes, dust for finger prints and find clues in ransom notes.
Children also got the chance to carry out police style interviews and officers from Harrow Police were on hand to give the youngsters expert advice on how to investigate a crime.
Eight teachers were questioned in connection with the murder and were forced to have their mug-shots taken and watch CCTV footage of their movements, which was used to build up the case.
Pupils then enjoyed themed food in the canteen with staff joining in the fun. At the end of the day a school assembly was called and the guilty person, who turned out to be Mr Green's wife Ms Nasser Green, was handcuffed and taken away.
Neha Dave, 15, and Kalpana Balaskandan, 15, enjoyed working together to crack the murder.
The event was organised to get the pupils to learn how to investigate, work in groups and try and problem solve.