In May 2015, Christie’s sold Pablo Picasso’s “Women of Algiers” for $179.4 million, the highest price for a painting at auction up to that point. Two and a half years later, Christie’s sold Leonardo da Vinci’s “Salvator Mundi,” a portrait of Christ, for $450.3 million. In his new book, “The Last Leonardo,” the author and documentary filmmaker Ben Lewis writes about the painting’s twisty, contentious road to the auction block and beyond.

“Salvator Mundi,” Lewis writes, is “poised between the medieval and the modern, an image that opens the door to the new world, just as Leonardo himself did.” But it remains the subject of controversy, its whereabouts unclear and its authorship still disputed. “It has become a victim of the secrecy upon which the unregulated art market, and around it the 21st-century globalized economy, is built,” Lewis writes. Below, the author talks about how writing this book was a dream job, the surprise of telling a previous owner of the painting about its ultimate fate, and more.

When did you first get the idea to write this book?

After the painting sold, in November 2017. I thought this was the most amazing adventure story a painting had ever gone through — the history of it, this 500-year purported history. It’s been in palaces and penthouses, and you’d expect that. But it also spent 50 years in American suburbia.

And we’re really not sure about its history. There are incredible blanks, and a lot of subterfuge. No painting I ever read about or studied — and I’ve done quite a bit of art history — has had so many ups and downs. Like Jeff Bridges says in “The Big Lebowski,” “There’s a lot of ins and a lot of outs.”