Not since the crablike stalk of Kevin Spacey’s Richard III has the star of a show had to adopt such painful-looking posture. In the title role of Martin McDonagh’s 1997 play, set on the island of Inishmaan in 1934, Daniel Radcliffe as the orphan Cripple Billy hoists one hip above the other. The leg from his higher side hangs almost uselessly while above it, an arm curls upwards like a withered vine. You’d think poor Billy would be the object of sympathy. But the strain of banter that passes between the people of Inishmaan contains little kindness and much casual cruelty. When Billy asks the local doctor if his mother was pretty, he tells her the truth — she was ugly enough to stop a pig.

It is this merciless doling out of harsh reality that keeps McDonagh’s play and Michael Grandage’s production from the sentimentality the play exists to undermine. When Billy attempts to escape through being discovered by an American director and his film unit who are shooting on location nearby, even Billy’s doting aunts hope the ship taking him to America sinks and that he drowns like his parents did when they rowed out to sea one night with sacks of rocks attached to their ankles. The play’s mystery is why.

The film scenario is real. Though we never see the director or crew, Robert Flaherty arrived in 1934 to make Man of Aran. McDonagh’s point is to subvert the cliché of rural innocence that was depicted by the film and has been promoted ever since.

Radcliffe serves the work well with a pitch perfect and modestly underplayed performance. But this is very much an ensemble piece. Pat Shortt is larger than life as the island gossip who, when not trying finish off his liver-diseased mother with alcohol, doles out news in exchange for eggs. Also outstanding is Sarah Greene as the pretty and violent Helen, whose childhood was spent inflicting injury on the priests who attempted to molest her. Death, abuse, grief and loneliness are the subjects of McDonagh’s comedy. But it’s the cruelty that gives it life.