Stepping into the shoes recently vacated by Lenny Henry, Sue Perkins proves to be the perfect guide through Every Brilliant Thing, playwright Duncan Macmillan’s touching and funny monologue about mental health and suicide.

It is told from viewpoint of a child who started compiling a list of reasons to be cheerful at the age of seven, when her mother first attempted to take her own life. Members of the audience are given cards with some of the entries written on, contributing whenever their number is called.

The audience participation in the intimate @sohoplace theatre goes deeper than that, however. Perkins calls on strangers to act as her taciturn father, her lover, the school counsellor who first got her to open up about her feelings via a sock puppet, and a number of other supporting roles. Others contribute props.

She deals with these interactions in a genuinely funny and endearing way – gently teasing people sometimes, but only to get the most out of them, and they all rise to the challenge. Her quick, personable wit builds a sense of community in the room, so crucial for a play that’s about the importance of connection and conversation. She engineers a playful mood in which a crap knock-knock joke suggested by her ‘counsellor’ becomes a moment of utter delight.

Yet despite the light touch, Perkins ensures the weight of the core story is never marginalised. The audience feel the gravity of the topic, but more importantly the optimism of the message as she negotiates a demanding 85-minute speech and the countless ad-libs.

Nor is the play, which was developed with the help of comedian Jonny Donohoe more than a decade ago, ever twee or cloying, a real risk for a show with a premise like this. 

The script accepts it would be naive to believe a list of all that is lovely – from ice-cream to Christopher Walken’s voice to  ‘the awkward dance of non-verbally negotiating whether it’s to be a hug or a handshake’ –  could cure someone of a severe clinical depression. However the suggestion that the act of compiling the catalogue helps the daughter, if not the mother, persists.

For the ‘social contagion’ of mental illness is one of the deeper topics addressed here, from the ‘Werther effect’ of copycat suicides – seen after the irresponsible reporting of high-profile cases, for example  – to the inherited sensitivity the offspring of the manic depressive can experience. ‘Deeper’ is comparative, of course, and there are many plays that drill more thoroughly into the experience of living with depression, but that is not Macmillan’s aim here.

The focus here is entirely on hopefulness, even in difficult times. The character’s childhood was not predominantly miserable, we are reassured, and the oft-repeated truth that ‘things will get better’ for anyone in depression. The uplifting power of this piece makes a very convincing argument for that.

• Every Brilliant Thing is playing at @sohoplace until November 8. Perkins is in the show for most of the rest of the month, with Donohoe, Henry, Ambika Mod and Minnie Driver taking other dates until it ends. Schedule  

• Samaritans are available any time. Call for free on 116 123, email jo@samaritans.org, or visit samaritans.org