You may be looking for the audio story.

The Old Rogue was a café in Catford, London owned by Sid. When Arkinen used the understanding device in an attempt to destroy the Earth, the beam hit Sid instead. Jamie McCrimmon pushed Arkinen into the beam and he swapped bodies with Sid.

The Second Doctor left Arkinen to manage The Old Rogue in the hope that living among humans would rehabilitate him. Every decade he visited to check on his progress. On one occasion, the Fourth Doctor and Romana II visited but found Arkinen to simply be self-pitying. After they left, Katya, one of the employees, revealed herself to be a mercenary searching for Arkinen. She wanted to restore him to his rightful place as emperor. Arkinen refused, claiming to simply be Sid. (AUDIO: The Old Rogue)

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