Freddie Thornhill (Sir Ian McKellen) and Stuart Bixby (Sir Derek Jacobi) are an old gay couple who have been together for nearly fifty years. Their lives now revolve around entertaining their frequent guests and hurling insults at each other at every opportunity.
Presumably it took almost two years for Vicious to return in order to negotiate high enough fees to coerce such accomplished actors to come back. We must hope that in future their many, infinitely superior, other projects delay the process even longer.
As fun as de la Tour and Rheon are, though, McKellen and Jacobi are the heart of the series, which is the first UK sitcom to feature a homosexual couple at its core.