Horrid Henry’s Stinkbomb (Horrid Henry #10) by Francesca Simon

A stinkbomb becomes a deadly weapon in Horrid Henry’s long-running war with Moody Margaret; he uses all his guile to win the school reading competition, only to find the longed-for prize is not what he expected; he goes for a sleepover and retreats in horror when he finds that other people’s houses aren’t always as nice as his own; and he has the joy of seeing Miss Battle-Axe ticked off by the Head when he knows it was all his fault. In short, another vintage HORRID HENRY title!