Tower of London, 1601:
Henry Wriothesley, third earl of Southhampton, sits in his cell awaiting his death for conspiring to overthrow Queen Elizabeth I.
Meanwhile, back at Southampton House, where the Earl would have been snugly at home, his cat Trixy wants to know where daddy is. After a while, the distraught cat leaves home and strikes out for the big city, finds the Tower, and finds the Earl, where she hung out with him for two years until a change in rule frees the Earl - and his cat.
True story, thought it's very possible Trixy got some help getting to the right cell. I got this story from 100 Cats Who Changed Civilization, by Sam Stall (2007: Quirk Books). After his release the Earl had a portrait done of himself and his staunch cat. (Thanks, Elizabethan Geek. Coolness.)