Martin Moon (David Rawle) is a twelve-year-old boy who lives with his family in Boyle, Ireland in the late 1980s. His imaginary friend Sean (Chris O'Dowd, The IT Crowd) helps him cope with the challenges of growing up, such as dealing with school bullies and his three older sisters. Being only imagined by a boy Sean's comments are often naive and comical, as the advice he imparts on Martin, is often not very good. References to popular culture, especially films and television series are frequent and add authenticity to the contemporary late 1980s feel of the programme.