In 1935 a group of seven men meet in a London Club to celebrate the refurbishment of the Sennocke School's icon, a small stone shield presented to the school by Henry VI. The men have clubbed together to pay for the restoration but one of the number suggests that perhaps a more lasting contribution be made to the school in the form of a 'tontine.' Each of the members contribute to an endowment policy, the responsibility for which passes from each member as they die until such time that the last member dies and the endowment is made over to the school. It is hinted at that the continued upkeep of the shield may have a bearing on this.

The time then jumps to the mid-eighties and Sebastian Barton-Brooks a sporty and colourful member of the school and Goodfellowes House steals the shield during the end of term service. He leaves a verse carved into the fireplace at Goodfellowes and leaves to embark on a gap year mountaineering. It comes to light later that he disappears during this expedition and the secret of the shield's hiding place dies with him.

The action moves to the present day and Monty Maudsley has just passed into Sennocke School and we meet him on his first evening at Goodfellowes' House a boarding House set some way from the main school. The scene is set and by the morning of his first day he has not only seen the inscription but has teamed up with fellow new boy Herbert Mint. On his way back from the school a fellow member of Goodfellowes fills him on the Barton-Brooks story. Fuelled by this and having read an inscription on a war memorial in the local church he sets out to recover the shield. He enlists the help of Herbert who is academically stronger than Monty. The point is made that Monty struggled to get into the school and at times struggles to keep up. He is however a practical and pragmatic soul with a supportive family background.

The boys soon encounter Wolfy Blitzberg an unpopular member of staff who does his best to make all the boys lives a misery. Due to a punishment he sets Monty and Herbert the boys have to stay late at school. A fellow boarder invites them over to another house and whilst playing Monty stumbles over the answer of the riddle inscribed in Goodfellowes. It turns out to be a paper chase style trail left by Barton Brooks and the boys uncover another riddle which they resolve to unravel.

Meanwhile the last member of the tontine has died and Mr Pockett a local solicitor arrives to explain to Mr Littleboy, the Headmaster, that the school is due to receive an endowment. This news comes out of the blue and is well received until it transpires that to receive the money two words carved in the back of the shield must be revealed. Mr Pockett knows nothing of its disappearance and neither does the Headmaster let on. Instead he engages Wolfy Blitzberg, whose job is under threat due to his unorthodox policing of the school, to find the shield.

The boys have more success with the second verse and move on to a third despite several false starts. Wolfy has less luck, and also a false start. As a result the Headmaster engages Brad St Sure, a private investigator, to take over from Wolfy. This meets with strong opposition from Wolfy but eventually the two join forces. Brad turns out to be a confidence trickster and eventually disappears having stolen various things only to be caught by the police and even the Headmaster spends a night in the cells.

After another false start, the boys solve the last clue, aided by a girl from the top of the school (Limmi who hails from Delhi) that Monty has befriended. The last clue pinpoints a final message which Wolfy overhears. There is then a race to the final clue which has been destroyed. The boys figure out a way of turning back the clock and are given clear instructions as to where to find the shield. The shield is uncovered but there is a twist in the tale.