This is essentially a mini war movie--or, more accurately, a prevent-a-war movie.
While checking on a missile silo (as I've said, they seem to have a lot of them out there) the Seaview discovers that the missile is missing. Nelson and Crane immediately set out in the Flying Sub to try and track the thief, leaving Chip Morton to investigate the rest of the silos in sequence.
Discovering a submarine in the vicinity, the Flying Sub moves in for a closer look--and is promptly shot down. Crane manages to exit the sub safely, but Nelson is knocked off his feet and cannot jump before the sub hits the water. By some miracle, he survives, although the sub itself is totally wrecked.
Nelson is picked up by the destroyer Macklin, and immediately commences a search for Crane. However, after he learns from Morton that more missiles are missing, he's forced to call off the search to concentrate on finding the missile thieves. Nelson's concern for his friend is evident, but he pushes it aside--there's no time to mourn now.
Crane, meanwhile, has been picked up by the enemy sub. He too is concerned for his friend--one of the first things he asks is if they had picked up another survivor. From Captain Ruiz's statement, it seems fairly certain that Nelson is dead--but Crane doesn't have time to dwell on it, either.
Interestingly, while Michael Ansara makes a perfect villain (he looks SO intimidating) he is not presented as some evil fanatic out to take over the world. His country is trying to raise their power status in the eyes of the world, and he is simply a man doing his job, as are his men. He sees Crane as a useful source of information--after his current job is done. No one gloats or taunts Crane, and while they rough him up some when he fights them, it's only to stop him. There's no unnecessary torture. There is a rather stark contrast between Ruiz's men and the crews of the Seaview and Macklin--Ruiz's crew are unshaven, unwashed, and obviously haven't changed clothes in some time. (One can only speculate on how Crane found the atmosphere in that enclosed space.) One gets the impression of an old submarine, with very limited resources where the men's comfort is concerned.
The pieces line up on their sides of the board, and the game begins. Ruiz makes the first play, and nearly the last--he damages the Macklin severely, and kills the captain and his executive officer. Ensign Raser is stunned at suddenly being left in command, and is probably very grateful for Nelson's presence. Nelson gives a superb display of just why he's an admiral--in a matter of moments, he calculates how long it will take for the sub to come about and launch a second attack, and precisely works out a counter-maneuver for the Macklin, before turning to the little matter of dismantling a live torpedo jammed through the hull. The second attack is a clean miss. There was something eerie about seeing those torpedos flash by the ship, while the Macklin's crew stood silently watching.
Play and counter-play, back and forth. Crane is the random element, working desperately to sabotage the sub's efforts although it will likely mean his death. His first ploy is very effective--smashing the sonar equipment so that they will have to rely on the less accurate hydrophones. This gets him knocked out for a while, and he's oblivious to the depth charge barrage the Macklin sends down. Once awake, he takes note that they are trying to hide by running silent, leaps up, and hits an alarm button. Unfortunately, this ploy fails entirely, thanks to the slow reactions of the Macklin's sonar man. He calls Nelson to listen to the noise, and when Nelson asks if he got a fix on it, replies that he hadn't even figured out what it was. It sure sounded like any ship's alarm I've ever heard, and it would have been reasonable to assume that any odd noise would be coming from the submarine. The man should have been getting a fix on it instead of wondering, "Gee, what do you suppose that is?"
Crane gets locked up this time, and promptly gets free and takes to the air ducts, and starts banging around to say "We're down here!" A man is sent in after him, but Crane deals with him briskly.
Seaview is too far away to assist, and there are no other ships in the vicinity, so the Macklin continues the game alone. They do seem to cause some damage to the sub--although Nelson speculates that it might be a trick. There is a creepy moment when the Macklin crosses right over the sub, while the sub's crew stands and listens to the sound of it churning overhead.
Ruiz has been hugging the bottom, risking the destruction of his sub, whose crush depth is naturally far less than that of the Seaview. Listening to the sub creaking in protest is rather unnerving. It's not clear just how much time passes at this point, as Ruiz waits for darkness. Some of his men search the sub for Crane, to no avail.
Ruiz's precise calculations for his final assault on the Macklin sound remarkably like Nelson's from earlier in the day. He sends up a decoy periscope--and Nelson falls for it, stating that the sub captain had made his first mistake. When the torpedos close in, Nelson's look of resignation is his only acknowledgment that the mistake had been on his part.
There's no time for self-recrimminations. Nelson counters incredibly fast, ordering the ship evacuated while retaining key personnel on board. These key men are sent on their way once they've done their jobs, leaving Nelson alone to aim the crippled Macklin directly at the sub.
Meanwhile, Ruiz and his crew HAVE made a bad mistake--every one in the Control Room had gone topside to watch the destruction of the Macklin, leaving Crane free to emerge from the ducts. When Ruiz and his exec rush back down to submerge, Crane prevents them from doing so, shooting the exec and wrestling frantically with Ruiz as the Macklin smashes over the sub.
Nelson spots Crane as he crawls out on the remains of the sub, although how he recognized him in the dark and smoke and fire is beyond me. I loved Crane's look of astonishment as Nelson hailed him. Nelson throws him a rope, and Crane hauls himself onto the Macklin. Their delight at finding each other is necessarily restrained by the rush to get off the two ships before they blow up.
I'm not sure just how they were able to figure out just which "small country" had attempted to become a large country, but they did so, and the U.N. will see that they pay for their impudence. Crane comments that knowing that would have been small comfort for him personally if he had gone down with the enemy sub. Nelson zings him by commenting on the trouble HE would have had in getting a new captain. I wish that Crane could have had a better answer for him, but then, people so seldom are able to quickly think of snappy comebacks. Crane probably came up with a great line--at four o'clock the next morning.