Stayed up all night reading “The Believers,” it was that good. I knew I was in for a treat from the opening set piece at a London leftie party, and hungrily raced through it, finishing when the sun was coming up. Oh sure, I prolly could have savored Zoe Heller’s caustic prose a little longer, but her writing was a tonic for my frazzled soul. I didn’t want to put it down.

Certain critics have taken issue with the acerbic femmes dominating the book — these are not shiny happy people — but I found them quite amusing and surprisingly sympathetic. They may be judgmental snobs but they inflict as much misery on themselves as they do others. And they’re not nearly as creepy or malevolent as Heller’s censorious Barb in “Notes on a Scandal,” played so memorably by Judi Dench on the bigscreen.

Heller does a good job satirizing New York lefties and ascetics who consider themselves above sensual pleasures, serving up hapless Karla, a compulsive overeater, as the counterpoint to her reformed fattie mom and her forbidding sister Rosa. (Adopted drug-addicted sibling Lenny is the opposite extreme.)

The entire Litvinoff household revolves around charismatic lefty lawyer Joel, who has a debilitating stroke early in the story. His illness and the revelations it brings causes each character to come to grip with their own beliefs — political and religious — giving the book its title. Over the course of “The Believers,” each character reveals just enough to suggest how they dug themselves into their own particular hole.

The explanations don’t always add up: We’re supposed to believe, for example, that Audrey’s brash manner, developed as a coping mechanism as a teenage bride new to America, curdled into resentment at her husband’s infidelities and boredom with motherhood. By the time she realized she had become “a middle-aged termagant,” it was too late, Heller writes. That’s a little pat. But at least Heller doesn’t sugar coat or sentimentalize the behavior, like so many other writers would be tempted to do. And she suggests that Karla, patronized as caring by her family, isn’t quite as sympathetic as she seems, either, although this revelation doesn’t go anywhere. (Does the social worker really want to be a lawyer like her father, or does she want to surrender to happiness with kindly newsstand owner Khaled?)

Michiko Kakutani criticizes the book as a larger and messier undertaking than Heller’s previous two books, lamenting that “The Believers” lacks the “coiled and narrative suspense” of “Scandal.” That may be. Her latest tome is bookended by two hilarious set-pieces, but the wit is not sustained at that same high level throughout; impatient readers can barrel through middle passages quickly to find out how it all turns out if so inclined.

Nonetheless, it’s a good read. I can’t wait to go back and discover what I missed in my fervor to finish the story.