One of the most famous mystery writers of all time was embroiled in a mystery herself.

In 1926 Agatha Christie disappeared for 10 days, and crime solvers are still pondering what happened to her. One of those is historian Lucy Worsley, who is best known for her historical treatises on PBS where she dresses like a courtesan and waxes eloquently about the secrets of British royalty.

This time it's the English writer who gets the historian once-over with "Agatha Christie: Lucy Worsley on the Mystery Queen." Airing in three parts, it premiered at 7 p.m. on Dec. 3 on TPT, Ch. 2. Episodes also can be streamed at after they air.

In the documentary Worsley penetrates the question of Christie's disappearance. But it's no mystery, she insists.

"To say that she never spoke about the disappearance again is absolute rubbish. She told millions of readers of the Daily Mail what had happened at that moment. She was just about to go to court for her divorce, and she wanted custody of her daughter," Worsley says.

Christie, who had not said anything about it up until then did not want to have her secrets exposed but wanted to put it right, surmised Worsley, who wrote the book "Agatha Christie: an Elusive Woman." "So I'm sure she thought, 'I need to tell the judge in my divorce case that I'm not a bad mother, that I had the interest of my child at heart in what I did.'"

Worsley thinks that the vanishing may have been a suicide intent.

"She got a lot of criticism for having left her daughter behind. But if you are thinking of taking your own life, what do you do? You leave your child in safe hands, and you get out of Dodge. You protect your child by putting distance between you and your child," Worsley says.

It might have been a stunt to gain attention for her cause, but whatever it was, Christie did earn custody of her child.

"There's a lot of people who still believe that she did this on purpose to frame her cheating husband for murder, or to get publicity for her books, says Worsley, who calls it an injustice that Christie's story is still disbelieved.

Even though the mystery author's personal story is up to question, her writing is not. Christie went on to become the bestselling author of all time with 66 detective novels and 14 short story collections. Among her colorful characters, the most indelible remain crime solvers the Belgian Hercule Poirot and Miss Marple.

Miss Marple, with her omnipresent knitting bag and lumpy clothing, became an alter-ego for Christie.

"So in later life, she'd very often appear in a tweed suit, quite literally, and she'd say, 'Oh, little old me. I don't know how I wrote all of these books. It all seemed to have happened by accident.'"

Miss Marple could say things that Christie couldn't, according to Worsley, who likes the dowdy character because she stands for Christie. Both Marple and Christie get older at the same rate after World War II and they use some of the same strategies to misdirect our attention away from what they're really capable of being.

"Very occasionally, Miss Marple says things like 'Women must stick together.' That's something that Jane Marple says that Christie probably wouldn't say. Well, she hasn't said it in the records that survive," Worsley says.

But Christie wasn't always compliant. She was known to be "as hard as nails" when she was working with her agent or publisher.

"Oh, she wasn't fluffy old Miss Marple in her professional dealings. No, no, no. She had a demon work ethic and a very good sense of her own worth," Worsley says.