It started with $5 and an armful of used books scoured from the shelves of Biblo & Tannen’s on booksellers row. And it looks like it will end with a 1929 first edition of Dashiell Hammett’s “Red Harvest” worth $60,000.

Otto Penzler, the owner of The Mysterious Bookshop on Warren, has put his collection of mystery fiction – 55,000 titles, the largest in the world – on the auction block with Heritage Collections here in the city. Up for grabs will be a first edition of “The Big Sleep” signed by Raymond Chandler and Hammett’s “The Maltese Falcon,” both worth at least $30,000, the auction house estimates.

The whole thing is giving Penzler, who has had his shop here for 13 years, major pangs.

“I’m depressed,” said Penzler, sunk into an armchair in his (what else) booklined office in the basement of the shop. “My plan was to live forever. But it occurred to me God might not have the same plan.” He’s 76 and healthy, so he’s also worried he made the wrong decision. Hard to know.

Penzler was a cub reporter covering sports for the Daily News in 1963 when he started his collecting habit with a copy of Sherlock Holmes. He’d give himself a budget of $5 a week (he was making $42 a week), coming home sometimes with a dozen books at a time. Mysteries, he said, were the antidote to the brain-busting reading he did as an undergrad English major at UMich. But he then saw the magic in them.

“When you get to the good stuff, it’s fabulous. It’s every bit the equal of Hemingway and Faulkner and the great names of 20th Century literature,” Penzler says. “The Maltese Falcon, The Thin Man – these feel as fresh as anything being written today.”

His first shop (opened on Friday the 13th) was housed in a six-story building he bought for two grand behind Carnegie Hall in 1978. He moved the business to Tribeca – along with the nerve center for his four mystery publishing companies that he opened along the way – when he sold the building. It took three years, but he eventually built himself a dream library to house the collection, a wing off his house in Kent, CT.

He’d like to collect something again but doesn’t know what. And, he’s not sure he can bring back that feeling either way.

“I had the greatest collection in the world,” he said, “so to put together a so-so collection is not really interesting to me.” For now, he’s closed the door on the library.