Last year, we saw former the thick of it co-star Chris Addison reunite with Peter Capaldi. This year we will see Rebecca Front.
Front will guest in the two-part adventure that sees the return of the Zygons, details of her role are currently being kept a secret but she is thought to be playing a member of UNIT.
The episodes have been written by Peter Harness and will see the return of fan favourite Osgood (Ingrid Oliver).