You have to give Christopher Guest credit: When he finds a comedy style that works for him, he sticks with it.

Since This Is Spinal Tap in 1984, he has devoted himself to deadpan mockumentaries like Best in Show and Waiting for Guffman, using a loyal troupe of improv-adept actors including Michael McKean, Fred Willard, Catherine O'Hara, and John Michael Higgins.

In his new eight-episode series for HBO, Family Tree, premiering at 10:30 p.m. Sunday, Guest uses his oft-imitated technique (e.g., The Office and Modern Family) to trace one man's absurd genealogical search.

The naturalistic rhythm makes for a slow but frequently sharp sitcom.

After being dumped, Londoner Tom Chadwick (Chris O'Dowd of Girls) is in a holding pattern. When his sister asks why he isn't seeing someone new, he mordantly says, "Women would only get in the way of my wallowing."

It takes a trunk full of family artifacts and memorabilia to rouse him from his lethargy. He sets out on a quixotic quest to find out more about his relatives. Ah, the road to hell . . . .

Tom's is a tree better left unshaken. A series of false hopes and bizarre coincidences lead him further and further into the freak show that is his lineage.

In Tom's irradiated nuclear family, you have his dad (Michael McKean, wielding a variable British accent), who left his career as a Beefeater (Yeoman Warder) to fashion truly dreadful domestic inventions.

Sister Bea (Nina Conti) carries a little plush "talking" monkey with her everywhere. The puppet, who says the things she cannot say, is a font of wounding candor, breathtaking inappropriateness, and blunt expletives. Conti's background as a ventriloquist helps make this bit kill consistently.

Guest's projects are always set in a mad, mad world. Friends, Rastas, countrymen - everyone in Family Tree is extravagantly unhinged.

The first four episodes are set in Britain, which means that Guest's usual pageant of eccentricities has a strong flavor of English dottiness.

In the second half of the season, Tom goes off to investigate the American wing of his family, a convenient contrivance that allows Guest to bring aboard regular cohorts like Fred Willard, Bob Balaban, and Ed Begley Jr.

The split setting suits the circumstances of the series' cocreators. Guest, born Christopher Haden-Guest, is in fact the fifth Baron of Saling in Essex, a title he inherited from his British father. And Jim Piddock (another member of the Guest repertory) is an English actor who has spent most of his career in Los Angeles.

There are a couple of piquant recurring jokes in the first episodes: Tom's father is an enthusiastic fan of some terrible (and apocryphal) British sitcoms from the '70s, There Goes the Neighborhood and Move Along Please. We're treated to multiple scenes from these punchless programs.

And Tom is fixed up with some blind dates that are so crazy, you can't believe he sticks around for the entrée.

Compared to more aggressive American sitcoms, Family Tree putters along, but winningly. Consider it a somewhat daft cool-down from its 10 p.m. lead-in, Veep, which gets funnier every week.

Family Tree

10:30 p.m. Sunday on HBO