| Tessa |
|Behind the scenes|
|Appearances||"The Sign of Three"|
|Portrayed by||Alice Lowe|
Tessa approaches the duo during John's stag night in a flashback seen during John's wedding.
Sherlock and John return from John's stag night drunk, despite Sherlock's planning beforehand, and are interrupted by the arrival of Tessa, who wants Sherlock's help as she thinks she has just been on a date with a ghost.