Three Days Of Rain, Apollo Theatre, London

There's a lot of rain about on the London stage at the moment: Pete Postlethwaite is caught nightly in drizzle as King Lear at the Young Vic; Janie Dee fantasises in a downpour in Alan Ayckbourn's Woman in Mind at the Vaudeville; and the rain it, well, raineth every bloody day in Twelfth Night at Wyndham's.

And now soap stud Nigel Harman could do with some soapsuds as he flexes his pecs in the wet stuff in the revival of the American Richard Greenberg's cunning comedy Three Days of Rain, already dubbed "sheer theatrical Niagara", and proving the shower power of not only Harman but also James McAvoy and Lyndsey Marshal.

These three very likeable actors play two sons of architects and the sister of one of them in the first act; then the two architects and the wife of one of them in the second. All are played at the same age, around 30: the first act occurs in 1995, the second in 1960. As Greenberg says, "there is some assembly required because it's almost a mystery". One architect has died and his son Walker (McAvoy) has stumbled on the abandoned loft in Manhattan where the practice was forged. The draughting-board, the old bed, the whole play in fact, comes bathed in a sound design by Matt McKenzie that sounds ominously like Michael Nyman; it must be in the draughtsman's contract.

Designer Soutra Gilmour provides a magnificent eyrie, all steamed-up windows and grey brick. Here, Walker and his sister Nan talk on the day of the funeral, and Harman's Pip, a TV personality, chips in with his own theories about what should happen to the old house the partners designed together. It is all fairly diverting, and the dialogue is witty and pacy. Key to the second act is the discovery of a diary in which the first entry, "Three days of rain", when unravelled – there's a big argument and a stormy liaison brought on by that rain – explains why Walker wants nothing to do with his father's house.

Jamie Lloyd's production is a fully charged Donmar-style job, but there is an element of "so what" about the play, despite the best efforts of Harman and Marshal, who offers a brilliant double of accommodating Nan and blowsy Southern bitch Lina. James McAvoy gives two beautifully nuanced, perfectly projected performances in each act.

To 9 May (0844 579 1940)