Happily married for more than a decade to charming Dad's Army actor John Le Mesurier (Robert Bathurst), Hattie Jacques (Ruth Jones) is at the height of her popularity when she is seduced by her handsome young driver, John Schofield (Aidan Turner) while filming Carry On Cabbie.
Despite the danger of a career-threatening scandal, when the film ends she can't bring herself to end the affair. Ironically, Hattie can conceal her secret relationship more successfully by moving Schofield into the family home when the attic room becomes vacant.
An eccentric love triangle begins as the two Johns find themselves trading roles of husband and lodger. Hattie uses all her charm and ingenuity to navigate the escalating family tensions and threats of public exposure, but ultimately she must make a heart-breaking decision - which will risk leaving her quite alone.
Hattie is a bittersweet true-life drama about a very English love triangle, and a celebration of an extraordinary icon of UK comedy.