Fantastic Voyage (1966)

I have to admit I kinda love the gonzo SF of the 60s.  Between this film and Battle Beneath the Earth, there's more inventiveness than you'll find in a dozen post-Star Wars space operas.  Not a lot of sense, it's true, but I can live with that.

It's the height of the cold war, and both the west and the Soviet bloc have developed technology that allows them to shrink matter. 'We can put an army on a teaspoon' our protagonist is told as he is inducted into this secret '... but only for an hour'.

The 60-minute time limit is a nice narrative tool not only because it provides the impetus for the story, but does double duty as the deadline on which our heroes must operate.  And I do mean 'operate'.  A Soviet scientist has discovered how to break the one hour limit and shrink things indefinitely.  He's defected to the west, but Soviet agents injured him in the process.  He's unconscious, with an inoperable blood clot that will kill him.  Or it would be inoperable, if you lacked the technology to miniaturise a submarine and its crew and send them literally inside his brain to do the work.

A medical team is assembled, including the only doctor capable of performing such delicate work, but there are doubts about his loyalty.  The agent who brought the Soviet scientist to the west is brought onto the team to provide security (and to be the outsider who needs everything explained to him, so the audience can get their daily recommended dose of exposition).  And of course, the entire mission will be on a one hour timer.  The team has to be removed by then or they will return to their normal sizes with quite catastrophic (and I imagine rather messy) results.

I do love the fact that in the film, the briefing for this fanciful bit of science fiction is given on an old-fashioned overhead projector.  Science!

Anyway, the team is inserted into the comatose patient, but if you think things are going to go as smoothly as they were outlined in the briefing, then you've never seen a movie before.  Setbacks and complications mean we get quite the tour of the human body, which is abstractly represented in a number of quite interesting and psychedelic ways.

As you might imagine there are some major scientific issues, especially when we get to the action-oriented conclusion.  The novelisation (by Isaac Asimov) apparently addresses many of these, though of course the central impossibility of the miniaturisation process remains.  But fundamentally, this is good, goofy fun.