The Fifteenth Doctor and Belinda

Belinda Chandra is another puzzle box companion, but somewhat different. Her primary motivation is to get home, and the Doctor finds he's unable to do that, harkening back to the early classic series in a way. Unfortunately, her story got cut short and mangled by behind-the-scenes events. Which is a darned shame, because Varada Sethu was on a serious hot streak, appearing in Doctor Who and Andor at the same time.