Matthew Stevens, and his long time friend, Harvey Shepherd, are both pupils at Higham House Priory, the local primary school in a pleasant village called Heathfield, in East Sussex.
The boys are firm friends - though of quite different character. Matthew is headstrong - often his undoing - while Harvey is of a more cautious, and practical nature. This never deters Matthew for long, however, when he has some daring plan in mind: with an insatiable curiosity, he is as a rule unstoppable, and usually manages to overcome his friend's doubts and fears.
One Saturday afternoon, Matthew persuades a reluctant Harvey to agree to a visit to an empty, old mansion on a large, nearby estate - said to be haunted according to word passing around their school playground, for what he describes as an 'adventure' - but even the ever-confident Matthew gets more than he bargains for.
The boys quickly find that the once stately old house has some unsettling ways to discourage intruders. Hair-raising incidents, and their encounters with near disaster, together make Matt's eagerly planned excursion an eventful and memorable one.
Matthew, as usual, at first takes little heed of warnings. However, soon, some strange force is urging him on into a far-reaching, unexpected chain of events, and even his confidence is for once badly shaken.
Though the outcome of their unauthorised exploration proves worthy of his plan, he is about to learn a sharp lesson on how his impulsive actions can deeply affect others.