Ruth Gregson is a one time passenger on MJN Air, though she traveled for free, and is the sister of CEO Carolyn and aunt to Arthur Shappey. She appears to have a long standing argument with her sister Carolyn who she hadn't spoken to for 15 years before her appearance in the series. She has fond memories of Carolyn's second husband, the implication being they may have slept together.
As a surprise for Carolyn's birthday, Arthur books the crew to take a flight to Helsinki, posing as a normal passenger, and invited Ruth, her husband Philip, and their annoying grandson Kieran. Far from making up after not speaking to each other for all these years, the two sisters bicker and quarrel all the way through the flight.