The Avengers (1961)

S3E7 The Gilded Cage

Steed devises an elaborate scheme to catch the criminal genius J.P. Spaggs, aiming to pilfer a million pounds worth of gold bullion. However, the situation takes a turn when two detectives show up at Steed's apartment and apprehend Cathy for the murder of Spaggs, throwing a wrench into his carefully laid plans.