The Hong Kong Repertory Theatre (HK Rep) seems particularly adept at dealing with abstract themes, ambiguous characters and the absence of a well-defined plot - in other words, plays where the audience is expected to work alongside the cast and crew in order to complete the picture, and each reading is as valid as the next person's. Among those productions in which the universal themes of longing, grief, isolation and the unforgiving passage of time are explored through poetic language and imagery, Lumination of the Forgotten and The Isle come to mind. Both plays, and perhaps not co-incidentally, are written by HK Rep's artistic director, Poon Wai-sum.

Sleep, staged in March, shares similar ethos. It's a Cantonese adaptation of a Hungarian play by the Nobel-laureate Jon Fosse, who is a master of communicating ideas without having to say them in that many words. His spare, luminous dialogues work remarkably well in the HK Rep-produced Cantonese stage adaptation, translated by Tang Sai-cheong - chiming with the sound of sea waves, gently lapping against the shore. In this case, the sea is both seen and heard. Seen through a large window in the background, a digital watery expanse going through its diurnal motions resonates with the play's broader theme of the universal, and cyclical, nature of the human condition.

The play opens with a pair of young couples who set up home in a house by the sea. After a point, the audience can sense that each couple inhabits the same space in different time frames, though fragments from their stories play simultaneously, or intercut one another. Curiously, the Second Young Man - portrayed with understated tenderness by Angus Chan - seems to be aware of the presence of the first young couple and even makes some sort of a connection with the First Young Woman, cutting across time, even as he drifts apart from his partner, the Second Young Woman. His natural empathy, or perhaps his imagination - probably both - imbue him with a heightened sense of alertness to the traces left behind by fellow human beings who preceded him.

And then two more couples - who seem to be an elderly version of the first young pair and a middle-aged version of the second young pair - are thrown into the mix. There are moments when older and younger versions of the same character share the stage, though cliches like them starting a dialogue are avoided, in keeping with the writer's reluctance to attach a specific identity to any of his characters. Perhaps the only relatively unambiguous character in Sleep is that of the Man who has an affair with the Middle-aged Woman, causing her marriage to collapse. It is fun trying to speculate why the production's director, Yau Ting-fai, chose to cast himself in the role of the outsider-disruptor figure. Was it meant to be an inside joke, adding a light touch, perhaps, to the rehearsals of a play dominated by the sobering themes of decay and mortality?

Pang Hang-ying as the forgetful Older Woman, on her way to a slow fade-out, deserves special mention for investing her character with an endearing childlike energy that is consistent with Kiki Cheung's younger version of the character. Yu Hon-ting, whose main job in the role of the Middle-aged Man is to observe the action from the sidelines - a bit like the chorus in Greek plays - ably demonstrates how doing nothing can suffuse a play with depth and meaning.