A horse walks into a bar.… David Grossman takes the opening line of an old joke for his title, which could be a signal of comedy to come; and indeed he strews his novel’s pages with punchlines — good, bad-taste and groan-worthy. But this is gallows humour at its darkest: Grossman beckons us into a basement comedy club in an Israeli town, and uses the world of stand-up to explore not jokes but the nature of guilt.