`Moone Boy' tells the story of young Martin Moone and the adventures he has with his friend, Sean Murphy (O'Dowd). Sean, however, isn't a normal school-age mate - he exists only in Martin's imagination. But he's still able to help Martin survive life as the youngest in the scatter-brained Moone family that also includes mum Debra, dad Liam, and a trio of loudmouth sisters. Martin's fantastical imagination comes to life in a variety of animations from the Oscar-nominated studio Cartoon Saloon, as well as in the ridiculous schemes he comes up with against Sean's better judgement.