Some of the singed books from Frederic Dannay's collection shown on Sotheby's website.

The jig is up!

In a twist straight out of a pulpy page-turner, a son says he discovered his late mystery-novelist father’s signed books had been stolen — after seeing them go up for auction at Soetheby’s, according to a new lawsuit.

Upper West Sider Richard Dannay — son of detective-fiction author Frederic Dannay — claims 33 of his dad’s signed books were stolen by his step-mom Rose, passed to her son Terry Koppel and eventually given to Sotheby’s for auctioning, according to a Manhattan Supreme Court lawsuit filed late Wednesday.

Richard says he didn’t even know the books existed until he got the brochure from the auction house on Nov. 18, 2016 which described the collection as “The Terry R. Koppel Collection of Ellery Queen,” the court papers say.

Frederic and cousin Manfred B. Lee penned successful crime fiction books together under the noms de plume Ellery Queen and Barnaby Ross. Frederic also founded, authored and edited Ellery Queen Mystery Magazine for 40 years.

After Frederic passed Sept. 3, 1982 his third wife, Rose, allegedly fought his will and two years later the case was settled with Rose making off with cash, a car and other items.

She gave up her right to Frederic’s literary works and agreed to turn over property from their house including “all Literary papers,” the court documents claim.

“Rose Koppel violated these provisions and obligations, and misappropriated and retained the Books and Additional Material in the Ellery Queen Collection, and on her death left the Collection to her son, Terry R. Koppel,” the suit alleges.

When Rose died in 2014 she gave the books to Terry who tried to hock them, according to the lawsuit.

“On information and belief, Defendant [Koppel] knew of and participated in the misappropriation, and after his mother’s death, consigned the Collection to Sotheby’s for public (and private) sale,” the papers allege.

Richard, the executor of his father’s estate, “had no knowledge of the misappropriation, or of the existence of location of the Books and Additional Material, until receiving a copy of the Sotheby’s catalog,” the documents say.

Sotheby’s is safeguarding the books and agreed to suspend any sales until the dispute was worked out, the papers say.

The copies — most of which are signed — range in estimated value from $700 to $5,000, according to Sotheby’s.

One titled “The Roman Hat Mystery” is an original from 1929 authored by Ellery Queen, which is valued at $3,000 to $5,000, according to the website.

Richard — who wants the novels back — claims Koppel has refused to turn them over.

Koppel did not immediately return requests for comment.