David Tennant is heading to Acorn TV, starring in their original series Deadwater Fell (April 6). Tennant plays a family man, whose wife and three daughters are killed in a house fire. But, upon further investigation, it appears the fire is a cover-up and they may have been killed prior. The question is put out there: whodunit? And, as TVInsider points out, it's also a "whydunit?"

Please be warned, Deadwater Fell has already aired in the U.K., so if you look it up online, you may come across the ending in headlines by accident (we learned the hard way).

We love a good cross-over. It's got us thinking, what other Doctor Who actors have stepped into mystery-thrillers? Here are ten DW stars and guest stars who put the Who in whodunits:

1. David Tennant in Broadchurch

We'll stick with David Tennant, the Tenth Doctor, to get the ball rolling. Before Deadwater Fell, Tennant starred as DI Alec Hardy in the BBC America original Broadchurch. He plays a troubled, yet dedicated detective in search of a child killer. He wasn't the only DW alum to pop up, co-starring opposite Olivia Colman and Arthur Darvill. As well, Jodie Whittaker, the forthcoming Thirteenth Doctor.

2. Billie Piper in The Sally Lockhart Mysteries

https://www.youtube.com/watch?v=-MJPdPdekZQ

Billie Piper, who played companion Rose Tyler to the Ninth and Tenth Doctors, signed up for two whodunits, adapted from Philip Pullman novels for TV. You can look for her in both The Ruby in the Smoke (2006) and The Shadow in the North (2007). Set in Victorian England, Piper portrays Sally Lockhart, who is investigating the mysterious death of her father. And, keep an eye out for Matt Smith, as this marks his TV debut (wowser!). It was before he became the Eleventh Doctor, but still counts. In the follow-up, Piper's Lockhart investigates a missing steamship.

3. David Morrissey in The Missing 

https://www.youtube.com/watch?v=DXiOwboL774

David Morrissey starred in the 2008 DW episode, 'The Next Doctor." His character, Jackson Lake, believed himself to be an incarnation of the Doctor. Alas, he was not. We also saw him in the second season of The Missing (2016), where he plays a heartbroken father whose young daughter was believed to be kidnapped. Years later, she unceremoniously wanders into town on her own. Her unexpected return sets off a lot of alarms.

4. Jenna Coleman in The Cry 

https://www.youtube.com/watch?v=nk7OM9-kplg

Jenna Coleman played companion Clara Oswald (and other incarnations) from 2012 -2017. She recently starred in The Cry (2018). When her baby goes missing, she and her husband (Ewen Leslie) are understandably beside themselves and go into a psychological spiral. Set in Australia, the search for what has happened takes them on a figurative and literal journey.

5. Olivia Colman in The Secrets 

Olivia Colman starred in the 2010 DW episode, "The Eleventh Hour." As mentioned above, she also starred opposite Tennant in Broadchurch, as his partner DS Ellie Miller. Prior to Broadchurch, we saw her in the 2014 series The Secrets. She took on the role of Pippa in the series opener, "The Dilemma." She plays a vet, whose mother (Alison Steadman) is terminally ill. Her mother asks her to help end her life, using the chemicals she has access to at work. It's not a whodunit, per se, but a willshedoit. You can watch a clip via BBC One here.

6. Bill Nighy in Ordeal by Innocence 

https://www.youtube.com/watch?v=39vocCC8P9c

Bill Nighy took on the role of Dr. Black in the 2010 DW episode, "Vincent and the Doctor." We also enjoyed him in the 2018 adaptation of Agatha Christie's Ordeal by Innocence. In the three-part miniseries, he plays Leo Argyll. The story is set in 1954 Scotland at Christmas time (it was based in England in the book, but the location has shifted). When the Argyll family’s matriarch (Anna Chancellor) is found murdered, it’s believed her adopted son Jack (Anthony Boyle) is guilty. He's then carted off to prison, with the rest of the family left in disarray.

7. John Simm in Trauma 

https://www.youtube.com/watch?v=aCMqwVk4GP0

John Simm played a major role in DW as The Master, starring in seven episodes from 2007 - 2017. In 2018, he took on another titular role, playing a father whose teen son dies on the operating table in Trauma. His son had been stabbed during a street scuffle, but when he entering the ER, he was saveable with routine surgery. But, he didn't make it off the table. Simm's character believes the surgeon (Adrian Lester) is to blame, having cocktails prior to operating. This may fall under a washeokaytodoit?

8. Alex Kingston in Chasing Shadows 

https://www.youtube.com/watch?v=gqk0qTIw9qA

Another major player in the Whoniverse, Alex Kingston, who played companion River Song from 2008 - 2015, pops up on this list. We also saw Kingston in the 2014 miniseries Chasing Shadows as Ruth Hattersley. She plays a social worker who teams up with a missing persons unit. Together they search for a serial killer. They know who is doing it, they just need to identify and find him.

9. John Hurt in The Oxford Murders

https://www.youtube.com/watch?v=ID5lJ32PveE

The late John Hurt was a welcomed addition to DW, starring as the War Doctor in three episodes in 2013. Prior to stepping into the Whoniverse, he starred in 2008's The Oxford Murders. The movie is based on Guillermo Martínez's novel by the same name. The story is set at Oxford University, where a professor (Hurt) and his student (Elijah Wood) work to solve a string of unexplainable murders, which are somehow tied together by mathematical symbols.

10. Maisie Williams in The Falling 

https://www.youtube.com/watch?v=8OEhqmKmZ9Q

And, finally, Maisie Williams joined DW in 2015, starring in four episodes, "The Girl Who Died," "The Woman Who Lived," "Face the Raven," and "Hell Bent." Prior to DW, Williams starred in the 2014 mystery-thriller The Falling. Set in 1969 England, a girl's school is taken over when a mysterious fainting epidemic breaks out. Instead of a whodunit, this one might be categorized as a whatdunit?

Now that we know the Who — WHICH one are you going to watch first?