Eddie and his mates were all looking forward to their Activities Week trip to Brains Bay. Before they are due to go, however, Eddie makes a shocking discovery. The so-called "fun-packed week by the sea" is merely a bait to lure the Year Nines away from their homes. Their teachers seem to have liaised with the enigmatic "Dr Gravesend" - but for what? All Eddie and his friends know is that huge profits are to be made from something in the students' brains. The four friends endeavour to find out what's going on and foil the Brains Bay plot. They must tread very carefully, for as Eddie finds out the hard way, Dr Gravesend does not take kindly to young eavesdroppers and spies.