Sean (O'Dowd) is the imaginary friend of 10-year-old Martin Moone, the youngest child of a family living in a small town in Ireland. Martin has a unique perspective on life aided by an imaginary friend. His imagination comes into play both in his childish drawings, which come alive through animation, and in the ridiculous schemes he comes up with, against Sean's better judgement. With Sean's help, Martin negotiates life as the youngest in a chaotic, scatter-brained family.