When Daniel Radcliffe, on a break from filming the Harry Potter series, stripped off for a stage role I was more shocked by his character smoking than the nudity. Now Matthew Lewis, the good-hearted, nerdy Neville Longbottom in the films, is playing a male escort and I found myself more shocked by the language coming out of mouth of Niamh Cusack's character.

Owen McCafferty's play links two couples: canteen supervisor Niamh Cusack and her husband of 30 years Tom (Sean Campion) with check out girl Tara (Ruta Gedmintas) and her boyfriend Peter (Matthew Lewis) via a chance encounter and a coincidence. The title of the play refers to more than the obvious relationship infidelities, it works on a much more personal level too: how faithful are we to ourselves?

Each scene is a conversation between two of the characters, through which it explores communication, relationships, truth and sex. McCafferty examines the idea that the person you are closest to, most intimate with is the person you don't necessarily talk to properly. It takes a shock in both relationships - one party breaking the routine, the accepted norms of behaviour to awaken a deeper understanding and appreciation of their partners and a better understanding of themselves.

The staging is very simple, a mirrored wall, a bed and two chairs which are moved depending on the scene but this is a play very much about the words and performances rather than props. The intimate space at the attic-like Found 111 is nearly perfect giving you the sense that you are eavesdropping on behind closed doors conversations.