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 an unique perspective on life aided by his imagination. 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 judgment. With Sean's help, Martin negotiates life as the youngest in a chaotic, scatter-brained family.