The monsters are causing havoc at Billy's best friend's birthday party.

It's Billy's best friend's birthday, and the Mini Monsters have come to the party too! Gloop gets mixed up with the jelly, Fang-Face is after the cake and Trumpet's been swept away by a balloon. Billy can't save them all on his own, but who can he turn to for help? Join Billy and the Mini Monsters in this laugh-out-loud adventure series for young readers, with colourful illustrations throughout.