BROOKLINE, Mass. – There’s a new mystery on Dennis Lehane’s mind, and the best-selling author is offering a special reward solving the case: Find his lost dog and get a spot in his next book.

The plot kicked off Christmas Eve, when the crime novelist’s rescue beagle Tessa escaped from his yard after an outdoor gate latch didn’t lock all the way.

Since then, Lehane’s family has launched an all-out search. They’ve posted fliers, organized foot searches and used social media to try to bring Tessa back to their home in Brookline, Mass., near Boston.

The 47-year-old author of books including “Mystic River” and “Gone, Baby, Gone” is offering a monetary reward and has said he’ll name a character in his next book after whoever finds Tessa.

Lehane said Thursday outside his home that he’s surprised by the media attention the story has attracted, and thinks it has something to do with the character offer.

But he said as word of the missing dog spread, his family has heard from people across the country on a “Finding Tessa” Facebook page.

They even got an offer of help from a dog psychic in San Francisco.

“No dog since Lassie ever got this attention … the flip side of the comedy is, who wouldn’t do this for their dog?” he said.

The doggie dilemma comes as Lehane faces a Friday deadline for finishing a movie script based on his short story “Animal Rescue,” timing he said may be “sadistic irony.” The movie is scheduled to begin shooting in March in New York City.

The author said he’s been spending about four hours a day searching for the tri-colored female beagle after he finishes writing, and his wife has dedicated about 10 hours a day to the effort.

They adopted the 4-year-old beagle not long ago from a Florida rescue agency. Before that, Tessa was a stray in Georgia.