Walt and Judy, of 1970s small-town Vermont, can't conceive a child. For all their mutual tenderness, life has become just "a collection of gestures and habits". So they adopt.
Specifically, they adopt an orphaned chimpanzee.
Yes, it's a jolting concept, and it means you can't read McAdam's third novel without feeling perceptions shift and conventions splinter.
Looee is from Sierra Leone, his mother killed by a poacher's shotgun blast; his own first months passed as an object of black-market smuggling. The adoption means initial salvation for him, and a challenging journey into courage and sacrifice for his human foster parents.
Right from the start there are people who scream, sneer, talk behind hands at the house's sweet, nutty smell, or who openly denounce Looee as an abomination.
But Judy and Walt are flooded with utter, if not utterly convincing, love.
They devote themselves to their remarkable child. They're sensible, strong, admirable people. None of this is enough to prevent the appalling catastrophe, the mutilations and maimings, which change every character forever.
As the narrative plummets towards horror and heartbreak, a new figure assumes prominence.
He's David the primatologist, expert in animal communication, challenger of humanity's claim to its unique status. He works for the Girdish Institute of Florida, a scientific centre tempted by market forces and mass media. The use of Looee and other chimpanzees in medical research (Aids is beginning its ravages) brings scenes that will make you swallow.
One of the novel's most startling aspects is the alternation between human and primate compounds and voices. McAdam's rendering of the thoughts and perceptions of Looee and others is daring, dramatic and remarkable in its approach, but variable in its success.
There are cosy parallels (I have to mention the Democrat chimpanzees and the Republican chimpanzees) and alien abysses. Violence threatens and explodes till the very end.
It's a deeply thoughtful book. The plot falters and clogs on occasions, and philosophy and polemic are inclined to take over: "Knowing I am an ape doesn't stop me from being an ape." (That's a human talking, by the way.)
Style is insistently lyrical-literary, stacked with metaphor, subversive with its punctuation and syntax, veering towards self-indulgence in tone and cadence. "A load of grief still sat in his chest and it would never properly be plumbed." Ouch. Or possibly glug.
But the engagement with Looee and his terrible trajectory is absolute, and absolutely compelling.
A brave, shocking and memorably tender story.
A Beautiful Truth by Colin McAdam (Granta $35).