The mystery writing team that created Inspector Rutledge and wartime nurse Bess Crawford to solve their puzzles has introduced a new character in a World War I-era love story for the holidays in “The Walnut Tree: A Holiday Tale.”

“Having seen ‘Downton Abbey,’ I think I a lot of people will enjoy this book while waiting for that series to start back up again,” said Caroline Todd, half the mother-son duo that publishes under the pen name Charles Todd. “Our heroine in this book could be a nurse and could get to see both sides of the war, through the eyes of these two men she becomes involved with. For the love story, that worked out very well. It takes a very special person to become a nurse in wartime.”

Caroline Todd will visit Aiken this week and will be the guest of honor at a book signing from 3 to 6 p.m. Tuesday at Booklovers Bookstore in the Country Square shopping center off Hitchcock Parkway. Copies of “The Walnut Tree” will be on sale, as well as copies of the Todds’ well-regarded Ian Rutledge series, now 14 books strong, and the newer Bess Crawford series of three books.

Said Caroline’s son Charles in a phone interview, “We wrote our first book, ‘A Test of Wills,’ in 1996, just as a lark. We were just doing it for fun, to see if we could, and we sent it to an editor we knew just to get some feedback. While we were waiting for that, we started on the second one, and suddenly we got a call back saying they wanted to publish it.”

The series begins in the postwar England of 1919, where Scotland Yard’s Ian Rutledge is trying to rebuild his life after wartime service, and hiding a dark secret. He’s convinced the doctors and the Yard that he’s whole and well and fit for duty, but in truth he struggles with what was then known as shell-shock and now is called post-traumatic stress disorder. In Rutledge’s case, the ghost of one of the men who died under his command follows at his heel and provides a Greek chorus for his investigations.

“We’ve developed Ian so much at this point he’s like part of our family,” said Charles. “Then Bess came along. We’d talked for a while about doing something different, but we knew we weren’t going to give up on Rutledge, so we waited until he was in a good position with the readers to start a new series.”

Said Caroline, “She was so interesting to develop – so different from Rutledge.”

Bess debuted in “A Duty to the Dead” in 2004. The Todds are preparing to launch new books in both series, “Proof of Guilt” starring Rutledge in late January and “An Unmarked Grave” starring Crawford in June.

They released “The Walnut Tree” on Oct. 30 to positive reviews and good feedback from readers.

Mother and son are both close friends with Booklovers owners Don and Fran Bush, and after the stress of bringing three books through the publishing process in quick succession, Caroline wanted a retreat, she said. Fran Bush offered her a place to take one, and to promote “The Walnut Tree” at the same time.

“I haven’t been to Aiken in quite a while, I’m really looking forward to it,” Caroline said.

“Last time I was here I spoke at the college, and I met so many interesting people.”

For more information about the book signing or to reserve copies of Charles Todd books for the event, call Booklovers Bookstore at 643-3198.