A safe containing the world's most deadly poison is stolen from MI9, and Stark assigns the MI High team to investigate its theft. Meanwhile, the country is being swept by a new craze - eccentric puzzle maker Quillian Pendrix has released his latest fiendishly hard puzzle and promised a tour of his puzzle factory and mystery prize to the first five people who solve it.

As Rose and Oscar search for clues, Carrie accidentally knocks over some dangerous chemicals and endangers the team. Feeling bad about the incident, Carrie finds her confidence sinking to an all-time low. Oscar discovers that one of the thieves who stole the safe works for Pendrix Puzzles, and on examination of the latest puzzle, Rose notices that its mechanism is similar to the lock on the stolen safe. Could Pendrix be using his contest to find someone who can open the safe and get the poison?

The team ask Stark for a warrant to search the factory, but he refuses. They realise that the only way to gain entry to the factory is for Rose to complete the Pendrix Puzzle and win a place on the tour. With only one place remaining, Rose stays up all night and eventually completes the puzzle, but is beaten to it - by Mr Flatley! Just when the spies are despairing, another contest winner is revealed to be a cheat and Rose claims the final spot on the tour.

In the factory, Pendrix reveals the safe door and challenges each contest winner to try their hand at opening it. Once again, Mr Flatley surprises everyone by solving the puzzle and opening the safe. Pendrix quickly ushers the contest winners away and the spies take the opportunity to steal the poison, but with guards and alarms everywhere, can Carrie conquer her nerves in time to navigate the poison to safety? Show less