Accompanied by Síle Súmaire, Murcha disobeys his mum, heading off into The Deep and boasting that ‘Great white sharks aren’t afraid of anything!’ However, that isn’t quite true! Murcha encounters all sorts of scary things, from ghost whales to dark caves full of mysterious creatures, and finds himself in plenty of trouble. But his naughty behaviour lands him in the deepest trouble yet and he discovers that the scariest thing of all is an angry mum!