There’s a lot of this sort of thing: gobbets of gossip tucked into every scene and wild happenings in the corner of your eye — a legendary and vengeful hairdresser dousing Linda Evangelista’s hair in petrol, say. It’s messy, and “fun fun fun,” as Stevens puts it, but there’s also a serious project at hand.

Late in his life, Avedon referred to himself as his own widow. He was consumed with securing his legacy — organizing retrospectives, even designing for himself a grand deathbed (which he never got to use; he died of a heart attack, at 81, on assignment in Texas in 2004). According to Stevens, he left the matter of telling the truth of his life to her. “Don’t be kind — I don’t want a tribute, I want a portrait,” he supposedly said. “Make me into an Avedon.”

Stevens does her best. She’s hamstrung by her affection for him, if mere affection is the word: She had him design her face-lift and slept next to a blown-up photograph of the two of them together. She doesn’t know what to do with the darker recesses of his life; the charges of his racism, for example, or of his youthful sexual encounters with his younger sister and his cousin. Avedon himself was surprisingly forthright about these relationships, but Stevens can only acknowledge what he told her, with a quick glance and shudder.

That said, she doesn’t spare him entirely. Avedon was famous for zooming in on his subjects’ warts and wens and liver spots, and he comes in for a little of the same. Stevens tells us about his reliance on uppers and downers and his fixation with his obituary in The Times. He’d count the words in the death notices of rivals and obsess over whether his would be longer (it would), whether it would make the front page (it would) or be above the fold or below (below, alas).

Stevens is most illuminating in her behind-the-scenes glimpses of the work. Avedon revolutionized the field; he brought an end to the era of the docile mannequin posing stiffly in this season’s clothes — his women leapt off the page; they danced and tumbled and communicated. “I invented a whole confetti of movement,” he said.