It seemed inevitable that Tom Baker would eventually tackle “The Prisoner of Zenda,” and this installment feels like a direct nod to Hope’s classic tale, with Colman, Granger, and Sellers having previously taken on the role. The Doctor and Romana find themselves on the planet Zenda as its hesitant prince, Reynart, is about to be crowned. However, the villainous Graft Grendel has his own plans for the throne, scheming…