Using a focused beam to pick up sounds from a distant reflective surface is real. In 1947 the Soviets developed the first interferometry microphone using infrared light. Switching to lasers greatly improved the system.
This was the first episode of the series to be filmed featuring Rhonda Parker as Mother's assistant. This is why in the first pool scene she smiles at Steed as if she has never seen him before.
The story focuses almost entirely on Tara King instead of John Steed.
In 1989 a book, 'Manifold Destiny', would be published; it gave instructions for cooking on the hot surface of a car's engine.