The narrative unfolds as the Doctor, played by Jon Pertwee, and the Brigadier, portrayed by Nicholas Courtney, are involved in an experiment alongside a scientist known for her psychic abilities. Simultaneously, Capt. Yates, brought to life by Richard Franklin, piques Sarah Jane’s interest with some unusual events occurring at a rural retreat overseen by a gentle Buddhist elder. These separate storylines inevitably converge as the meditators inadvertently connect with intergalactic spiders seeking a missing blue crystal—one that the Doctor has possessed for quite some time. Their goal is to enhance the power of their leader, allowing her to dominate the universe. The spiders are cunning adversaries and manipulate Lupton, played by John Dearth, in an attempt to locate the lost gemstone. Throughout this six-part story, the familiar team endeavors to confront these scheming arachnids, dealing with considerable psychic phenomena and high voltage situations. It’s nice to see Bessie reappear for a short while, and there's a good amount of action outdoors, including car chases, helicopter sequences, and even an appearance by a hovercraft. What ever became of them? The spiders don’t seem entirely believable, but the production designer did a decent job concealing the wires and magnets used in their creation; the use of electricity echoes the final confrontation in "The Raven" (1963). The ending carries a sense of melancholy alongside potential for what's to come, marking this as one of the stronger stories from series eleven.

Source on TMDB