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People find their paths in the strangest of ways.

— Mary to Joan, "The Leviathan"

Mary Watson is Joan Watson's mother. She is domineering and extremely strong-willed.


Season 1[]

Season 3[]

While working as Holmes' sober companion, Joan has lunch with Mary who is checking up on her. Mary insists that Joan come to dinner that evening as her brother Oren is in town with his girlfriend. Holmes uses the dinner as an opportunity to praise Joan which makes an impression on Mary. Mary visits the Brownstone and encourages Joan to pursue being a detective.[1] Several years later, Mary has lunch with Joan and says that her brother is having an affair. Oren denies this and questions Mary's mental health. Joan has another lunch with Mary who picks up on the insinuation and is angry. Holmes manages to convince Mary to see a neurologist by tricking her that she forgot Joan's birthday when she didn't.[2]

S01E10-Mary at Brownstone
I saw something in you.

S03E17-Mary waves
Crowbar, Watson.

Season 6[]

Joan receives a call from her father Henry that Mary is missing. She tells Holmes that due to Mary's Alzheimers she isn't supposed to drive but took the car. Mary arrives at the Brownstone, thinking she has a lunch date with Joan at a restaurant that closed 3 years prior. She calls Henry to tell him she's OK and thinks that she told him where she was going. Joan believes Mary is entering a new stage in her disease and suggested a nurse but Mary wouldn't speak to her for weeks after this. Later, Mary returns to the Brownstone and is having a good day. As Joan starts to insist hiring a nurse, Mary interrupts that they are interviewing nursing candidates. She's proud of herself and of Joan for caring enough about her to have such a difficult conversation. They make plans to have lunch.[3]

S06E14-Mary Watson
There are going to be more days like yesterday. But not today.


  • During an anthrax scare on a farm that Holmes and Watson are investigating, Mary texts Joan and tells her to throw away their milk as a precaution.[4]
  • Joan and Mary usually meet for lunch on the third Monday of every month.[2]
  • She hasn't read any of Henry's books, except his first one. Henry and Mary were married in 1980.[5]
  • Receiving a text from Shinwell Johnson, Joan lies to Holmes that it's a reminder from Mary to meet for coffee. Later, Holmes is able to deduce Joan's lie from the smell of the coffee on her clothes.[6]
  • Watson tells Holmes that Mary threatens people on restaurant review web sites.[7]


  1. Season 1, episode 10: "The Leviathan"
  2. 2.0 2.1 Season 3, episode 17: "T-Bone and the Iceman"
  3. Season 6, episode 14: "Through the Fog"
  4. Season 2, episode 20: "No Lack of Void"
  5. Season 5, episode 6: "Ill Tidings"
  6. Season 5, episode 22: "Moving Targets"
  7. Season 7, episode 6: "Command:Delete"