I recall really liking this science fiction show when I was growing up; back then, television options in Britain were limited to just three channels. Stephen Boyd, recognizable as “Messala,” is cast here in a different role, and finds himself aboard a submarine alongside “Cora” (Raquel Welch) and “Michaels” (Donald Pleasence), after they’ve been reduced in size. Their purpose is to be injected into a scientist's bloodstream, travel through his system, reach his brain, and use a laser to eliminate a dangerous blood clot. The process of shrinking things doesn't seem particularly remarkable, but about an hour into the story, the miniaturized objects begin to return to their original dimensions. The man they’re trying to help possesses the knowledge needed to maintain this reduced size, having previously offered it to the American government before a car accident—apparently orchestrated by a foreign power—left him in a coma. These brave explorers can't be inserted directly into his skull, so they must overcome the body’s natural defenses if they hope to save his life. It doesn’t take much of an intellect to realize that one member of their group isn’t working toward the same goal, and it’s not difficult to identify who that is. Naturally, these are a cooperative bunch, so will anyone notice before the mission is compromised? The performances aren't particularly noteworthy, but the plot provides the special effects team with an opportunity to craft a rather thrilling adventure while also presenting a less-than-pleasant view of our own internal anatomy; there’s a laser device, some unsteady sets, and treachery as well, all contributing to keeping things going after a somewhat slow start. It's not a brilliant film, but it possesses innovative qualities, and like “This Island Earth” from 1955, it holds a cherished place in my childhood memories.

Source on TMDB