So convincing is the ad-strewn half-curve of a Tube station platform that runs down one side of the Tricycle's stage into the distance that one almost expects someone to announce a delay to the start of the play.
But this setting, and an unseen suicide on the track - the one under of the title - is merely the starting point for a train of events that disturbs the life of Tube driver Cyrus.
Winsome Pinnock's watchable play moves back and forth over time as Cyrus tries to make sense of the tragedy. Meanwhile, a woman in a launderette finds herself subject to the unexpected attentions of a mysterious young Prince Charming (Daon Broni).
All this feeds into a skein of relationships that includes foster parents, a hit-and-run and a dry-cleaning ticket, as Cyrus - given the convincing air of an obsessive by Brian Bovell - latches on to conspiracy theories in the belief that the suicide was his son.
The poster for Pinnock's drama advertises this as an "emotional thriller that will send you hurtling through London's underground". Which is rather overstating the case, since Jennie Darnell's production has the urgency of the Northern Line on an off-day. But that's also partly because Pinnock's writing is rather gentler than that description implies - and none the worse for that.
Beneath her plotting lurk ideas of fate and coincidence, recalling that other Tube drama, Sliding Doors, and the feeling of urbanites adrift and searching reminiscent of Stephen Poliakoff 's Sweet Panic. The sense of family, too, and what it means for those whose home life was less than ideal, is also acutely evoked.
Although Pinnock may not have caused shock waves with this sensitive, if slightly sketchy piece (yes, mind the gaps), it does achieve the impossible in creating sympathy for a London Tube driver.
Until 5 March. Information: 020 7328 1000.
One Under
