One of three times the title does not begin "The Case Of The..."
Was filmed at the same time as The Case of the Bullied Bowler (1964) after Raymond Burr was released from the hospital.
The story is based on the rumors about Lake Toplitz in Austria. During the early 1940s the Nazis used the lake as a testing site for the navy. It is rumored that the Nazis dumped more than five billion dollars worth of gold and other treasure in the lake at the end of World War II. In 1959 divers recovered about £700 million in counterfeit notes the Nazis had planned to use to wreck the British economy. Searching the lake is difficult; it's about 300 feet deep and is littered with logs about halfway down. At least five divers have perished in attempts to retrieve more treasure. Despite its mention in the storyline of Goldfinger (1964), no gold has ever been recovered from Lake Toplitz.
Raymond Burr's participation in this episode is minimal - he doesn't even show up until almost the 20 minute mark.
In the previous episode, The Case of the Bullied Bowler (1964), Perry's absence was explained when Paul said he was "on a flight to Paris." This episode continues that idea by having him make a side trip to Switzerland.