When Nelson's beloved big sister goes missing on a school trip, Nelson is devastated – he's not that good at making friends and his sister is the only person he can talk to. His parents join the search party and leave Nelson in the care of his mad uncle Pogo. Uncle Pogo is the caretaker of St Paul's Cathedral and it is here that Nelson stumbles across a machine, invented by Christopher Wren and buried for hundreds of years. Designed to extract the 7 deadly sins, the machine had a fault – once extracted, the sins became living, breathing monsters who would then follow the sinner around for eternity (unless they ate him first, in the case of the particularly sinful). Nelson accidentally extracts 7 deadly monsters from his own little soul. Ugly, cantankerous, smelly and often the cause of much embarrassment, Nelson's monsters are the last thing he needed in his life, but at least they're fairly harmless (he's a pretty good kid, on the whole). When he learns of their individual powers he realises the monsters can be put to good use, and together Nelson and the Deadly 7 set out on a quest across the globe to find and rescue his big sister. Somewhere along the way, Nelson realises that he finally has friends, even if they are smelly, lazy friends who like smashing stuff up.