Frustrating, fascinating and potent, this promenade piece from the theatrical innovators Slung Low begins its eventful journey in the auditorium, where participants are divided into three groups and don large, uncomfortable headphones, through which a calm but creepy male voice murmurs: three storytellers will appear, but you will hear only one speaking — you must follow him or her.

A harassed businessman and a cadaverous Victorian street urchin arrived, but my group was greeted by a bright-eyed woman called Joy. As she led us through the streets of Islington via a leafy park, a church and a library, she told of a troubled upbringing, a lonely love affair and a baby called Angel whose survival was a miracle.

Last Seen is inspired by the phenomenon of people who go missing, but its approach is stimulatingly oblique. Joy is feverishly searching for a gate or doorway leading to her lost daughter. Along the route are portents: golden apple cores in a gutter, a forlorn golden teddy bear, an amorous couple in a golden phone box. There are sinister signs, too. We are tracked by threatening youths in hoodies and masks; a grim-faced nurse hurries from a house.

Joy’s tale, written and performed by the magnetic Lolita Chakrabarti, is an echo chamber of literary allusion, resonant of fairytales, Blake and Greek and Norse mythology. Angel’s celestial name also refers to the London location; glimpses of Robin Hood and Zorro among the trees suggest memories of childhood TV viewing — though these heroes cannot be relied upon here. Yet the spell takes effect only gradually, the difficulty of seeing Joy from among the crowd and of focusing on her narrative an initial irritant.

Patience, however, is rewarded; the thump-thump of your own footsteps — the only external sound audible through the headphones — begins to sound like an irregular, hypnotic heartbeat. Passers-by interact with the drama in unexpected ways: was the burly, bald man with two scary dogs an actor or just an unwitting but astonishingly apt extra? And the conclusion is a startling heartbreaker. An imperfect work, but wonderfully inventive, and transporting in every sense.

Box office: 020-7359 4404, to Sun

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