One night, deep in the catacombs of St Paul's Cathedral, eleven-year-old Nelson stumbles across a strange and ancient machine, which accidentally extracts the seven deadly sins from his soul in the form of living breathing, grumpy, smelly monsters. Suddenly he's stuck with seven angry, sneaky, greedy, vain, adorable, thieving, farting new friends, who help him form the best (and weirdest) plan ever: to find and rescue his missing beloved big sister.