A canvas bag is suspended above the stage, containing what? A load of rubbish, as we learn when it’s emptied. It’s an unconventional piece of symbolism in a highly conventional, and only fitfully convincing, domestic drama by the French playwright du jour Florian Zeller. Laurie Kynaston and John Light deliver strong performances as a tortured teen and his pent-up parent, the former torn apart by his folks’ separation, the latter trying to solve everything with manly optimism. One thing he can’t fix is the underwritten supporting roles: the stunned ex-wife (Amanda Abbington) and the stern psychiatrist hired when the boy’s self-harming turns serious (Martin Turner). The Son is the third in Zeller’s haut-bourgeois family trilogy. It’s often stirring, but provides little we haven’t seen before, even down to the gun, which you know will be triggered by the end.