Exploring a sewer near his home, David Hamilton encounters Alphonsus Tooms, a mysterious old man who warns him that the Forces of Chaos have targeted his neighbourhood, Trentham.

A supernatural steam engine takes David to meet the long-deceased Duke of Sutherland, who gives him the key to a hidden library. Here he finds a book containing a mirror in its centre. Thereafter, David and his new friend Helen are flung into a series of fantastical and dangerous adventures. Their school is terrorised by a witch and Trentham filled with bats before they're hung out to dry from the stars. But this is only the beginning of the longest day of their lives, in which they must battle demonic strangers, dragons, Wild Riders, giant blackbirds, spectral warriors and more.

Can the children defeat Chaos and restore their home town to sanity? All this and it's still only Monday...