In this inventive and ambitious piece of theatre, SharkLegs pulls off an impressive feat by making an interactive adventure story both touching and very, very silly. Gavin Plimsole finds out he has an incurable heart disease and withdraws to his shed to assess his life so far, and the life he might have remaining. Life is quantified in heartbeats, and this play asks us to think about what moments in our lives are the ones that really matter. Gavin’s experiments try to harness his heartbeats, truly appreciate them, and then share them with us.

Gavin’s storytelling brings the audience into the narrative through conversation and, more unusually, by giving each member of the audience a heart rate monitor which is projected onto the back wall of the stage. The scientific side of a story about our hearts is threaded into the narrative continuously and creatively. The audience are asked to join the experiment by raising their arms, thinking of a childhood toy, thinking about heartbreak, and the cast use the resulting heart rate differences to determine the outcome of the story they tell.

Rhys Lawton, playing Gavin, excellently manages the transitions between this interactive style of comedy and the narrative of his illness and personal crisis. There is continuous action taking place behind Gavin – red marbles zig zag down a track on the inside of his shed, and his two blood vessel companions take on the roles of the many characters going through his head. Richard Hay and Sarah Griffin in these supporting roles depict the childlike simplicity of Gavin (the toymaker) and of his story, and the dynamic between the three characters is consistently charming. The constant movement onstage makes the transitions between the starkly different modes of storytelling smoother than I anticipated, and it gives the simple narrative a strong momentum. There are a few moment where this seems on the point of stalling, as is the nature of audience engagement, but Lawton is skilful enough at managing the relationships between stage and audience.

The visual story-telling is commendable for being deceptively light-hearted. The symbolism of the objects he handles is revealed gradually, and becomes very poignant. When it becomes apparent that the red marbles are fragments of his broken heart – heartbeats – the strands of the story become beautifully tied up. Gavin the toymaker, storyteller, and heartbroken man become one very memorable character. Each audience member is asked to take away a ‘moment’, bequeathed to us by Gavin, in the form on a tiny marble in a box. This unity is what makes it such a satisfying and touching production.

In such an intimate production as this, which draws out an idea of our shared vulnerability and need for love, the small stage and size of the production is an integral aspect of the work. A clever sound design uses music and a soundscape of unusual noises made from flicking water and from rolling marbles. The closeness of the actors to the audience, though apparently making a few members of the audience a little uneasy (in that way that anything immersive can do), was what made it so resonant and tender.

The Inevitable Heartbreak of Gavin Plimsole is playing at Greenwich Theatre until the 10th September.