Passenger 2 (Spyfall)

On an aeroplane above the Pacific Ocean, a human spy received a package, in the form of a washbag, from another operative who claimed he'd found it in the aisle. She told him she was clumsy, and claimed that her sister was "always having a go at [her] for this".

Soon afterwards, in the privacy of the cabin restroom, she recovered a tube of Pearl & Diamond toothpaste, which contained a rolled up note within the cap, written out in code. She took multiple photographs with a camera built into her glasses, and then swallowed the note.

To her surprise, however, a Kasaavin emerged from the wall, setting off flickering lights, and attacked her. She was found unconscious in the restroom with her DNA scrambled to the point where she had become a brain-dead shell, human only in appearance. (TV: Spyfall)

Behind the scenes
In the credits to Spyfall: Part One, this character is only listed as "Passenger", while the other operative is given "Older Passenger".