Doctor Hess serves as the Head Mistress for the Kendricks Academy in England, a school used to train future Men of Letters operatives. In 1987, Hess called Mick and Timothy into her office and forced one of them to kill the other to ensure that they would follow the code absolutely. She handed them a knife, and to Timothy's horror, Mick stabbed him with it.
In 2017, while acting as a British Men of Letters Elder, Hess informs Mick that they don't have time to convince the American hunters to join them. She orders Mick to "assimilate or eliminate" and arranges her lackey, Renny Rawlings, to keep an eye on Mick.
Mick returns to the headquarters later on to find Doctor Hess with Arthur. Unlike before, Mick openly defies the British Men of Letters' code of conduct and chooses the Winchester way of doing things. His change in alliance convinces Hess that Mick has gone rogue, so she orders Arthur to shoot Mick point-blank.
While standing over Mick's corpse, Hess announces that the Winchesters must be eliminated and their efforts in America are a failure.
In Who We Are, Doctor Hess coordinates an assault against the American hunters. However, before they can act, a group of hunters including Sam Winchester, Jody Mills, Roy, Walt and Jerry attack the British Men of Letters compound, taking several losses but killing all of the British operatives. After killing Jerry, Doctor Hess retreats to the control room where she desperately calls for extraction, but is unable to receive it. At that moment, the hunters break in and Doctor Hess tries to convince Sam not to kill her, revealing the escape of Lucifer to him. Doctor Hess insists that the American hunters still need the British Men of Letters, but Sam refuses and shoots the computer Doctor Hess was communicating to Britain through. Calling Sam a bastard, Doctor Hess grabs her gun but is shot through the head by Jody before she can do anything.
After the American hunters attacked the British Men of Letters compound, a team led by Sam Winchester confronted Doctor Hess in the control room. After Sam refused Doctor Hess' plea to work together against Lucifer, Doctor Hess grabbed her gun and prepared to shoot Sam. Before she could, Doctor Hess was shot through the head by Jody Mills, killing her.
- Season 12
- Actress Gillian Barber previously portrayed Mrs. Rourke from the season 1 episode "Faith".
- Doctor Hess' name maybe a reference to Ruldolf Hess, Hitler's deputy.
- Her strict and deadly tactics in training children have led some fans to compare her to Dolores Umbridge, a Headmistress from the Harry Potter series. Indeed, even the Kendricks Academy which she is the Headmistress of loosely resembles Hogwarts, a school also from said series.
- She is the first Big Bad to be killed unreformed since Abaddon in Season 9.
- She is also one of the few Big Bads to be killed by a non-Winchester.
- While telling Sam about Lucifer, Doctor Hess repeatedly referred to Lucifer as "it". This may be the result of her disregard for angels in general.
- David Haydn-Jones believes Doctor Hess is one of the few people Arthur Ketch is afraid of.