Dick shows an interest in joining the Freemasons so the other doctors send him a spoof letter, allegedly from the Masons, inviting him to spooky Wookham Priory at midnight. Here they terrify him, before revealing themselves so when Dick issues an invitation to an orgy at the Empire Hotel, Duncan assumes this is a wind-up and rings the police. When the police turn up it's actually a masonic meeting which they interrupt - involving the Chief Constable. (thetvdb.com)