Netflix: Watch Instantly) and last night watched the 2008 episode "The Unicorn and the Wasp," wherein the Doctor and friend Donna Noble travel back in time to meet Agatha Christie on the eve of her real-life unexplained disappearance in 1926.)
"The Unicorn and the Wasp" is a clever mash-up of sci-fi and whodunit, loaded with references and allusions to Christie's works -- including Crooked House, Evil Under the Sun, And Then There Were None, and The Pale Horse. (Throughout the episode, Donna keeps referring to stories Christie hasn't yet written.) The episode is also very, very funny. Some clips below:
First, an important running gag from previous episodes ...
"It's the day Agatha Christie disappeared"
Donna accidently invents Miss Marple and the Doctor is poisoned
The Unicorn And The Wasp Trailer - ABC1
"The Unicorn and the Wasp" also has a nice write-up on the official Agatha Christie site.
P.S. -- Sorry to have been away so long. I do so much social media for my day job that it leaves little time to do it for myself. But with a whodunit of my own hitting stores in July, I'll have to get back on track ...