Adapted from Edward St. Aubyn's semi-autobiographical novels, the series opens with Cumberbatch's Patrick, a heroin addict, being informed that his father has died, forcing him to travel from London to New York to collect the ashes."If I'm to take control of my life, it has to be now," says Patrick, who is prone to an ongoing internal monologue with, among other things, the voice inside his head.What ensues, though, is a dizzying exercise in out-of-control addiction, allowing Cumberbatch to play drunk/stoned/high in a manner that's no longer the laugh line it was back in Foster Brooks' heyday. As for the source of his pain, that begins coming into focus in the second hour, which flashes back to his life as a young boy with his abusive father (Hugo Weaving) and his self-medicating mom (Jennifer Jason Leigh), during a wildly uncomfortable weekend in a chateau with several of his father's friends.There's a darkly comic streak in Patrick's plight, but also the nagging specter of the traumatic childhood that left him so damaged. The result is a series that's beautifully acted by an exceptional cast, and yet which won't be for everyone given its unrelentingly dour nature.As with the novel, there's an underlying commentary about the idle rich and their brand of debauchery, barely obscured by the polished marble and fine linen. The bigger picture, however, takes a back seat to Patrick's status as a walking time bomb, fumbling from one awkward situation the next, craving chemically induced relief.For Showtime, this handsome co-production with Sky Atlantic nevertheless feels like a coup, a jolting exercise in awards bait — premiering near the end of the Emmy eligibility window — featuring a versatile star (he's also been in a PBS movie and "Avengers: Infinity War" in the last month) at the height of his powers.The pay channel is using "Patrick Melrose" to inaugurate an expansion of its original series to Saturdays, and it's surely a shiny bauble to help get people's attention.Granted, in the way the episodes are presented, there's not necessarily a strong sense of momentum in Patrick's story. Thanks to Cumberbatch, it's nevertheless worth the investment watching him stumble along."Patrick Melrose" premieres May 12 at 9 p.m. on Showtime.