Some of these scenes are beautifully drawn, with the wit, pith and undercurrent of sadness characteristic of Harrison’s best work. (The opportunities and perils of A.I. as human companions were the subject of his play “Marjorie Prime,” a Pulitzer finalist in 2015.) The boy who gets the prosthetic finger is left at the workhouse because his family can no longer afford him. (Father to son: “Well. Goodbye, Tom. I don’t expect I’ll see you again.”) The reason the 1987 boy is grieving is that his bachelor uncle was buried that day. We don’t need to be told what he died of. But other scenes, like one set in 2076, when the last humans live as outlaws in a dystopia of semi-robot overlords, feel more like place fillers, necessary as steps in Harrison’s timeline but not compelling in themselves.