It starts in some unknown foreign country; the background music has an Eastern flavor, and there's a quick shot of what appears to be the outskirts of some royal enclosure. Two men enter a room featuring a large scale with a seat on one side of the balance. The men tamper with the scale; moving so quickly that they must have rehearsed it carefully beforehand. The scene switches to an outside shot with a very large crowd (that seem to be dressed in Western attire). Another unique feature: Admiral Nelson does a voice-over to explain the situation. Once a year (coincidentally falling around Christmas), the Lords of the Kingdom demonstrate their devotion to their king by weighing him on a scale and matching the weight with gold. In this case, unfortunately, their devotion proves deadly: as the scales balance, it sets off an explosion. (This could have been done a little better; the initial burst of smoke is very well done, but then they allow us to see the king simply tipping over backwards in his chair. Anyone who has accidently tilted a chair back slightly too far knows that can be startling and painful, but seldom fatal.)
The scene switches to California, with a man, woman and child riding in the back of a car. No words are spoken. The tension of the man and woman is shown up by their reaction when the boy begins experimenting on a toy flute. They only stand it for a few moments. Meanwhile, on the Seaview, we get a doubly rare shot; the crew's mess is filled with Christmas decorations, and the men themselves are nearly all in civvies. They're listening to carols over the intercom and quaffing a bit of Christmas cheer. We learn in passing that Curley comes from New England. He and practically everyone else is preparing to go home on Chrismas leave, although they should have started getting nervous when they learned that the Admiral and the Captain were in a meeting in the nose. A man from the State Department informs them of the king's death, four hours and thirty-five minutes ago. The assassination was part of a coup led by an anti-Western group, while loyalists called on the State Department to protect the king's heir, now travelling in California. For safety and security, the prince needs to return home by sea, and naturally the Seaview is considered best for the task, although they can't be ordered to do it. Nelson and Crane both know what the reaction will be if they refuse, so very reluctantly they cancel shore leaves and prepare to get underway.
When the prince is brought aboard, Nelson addresses the man, who is dressed in a military uniform. It's an understandable mistake; it looks like a family group. The man is the Prince's military advisor, Colonel Meger, while the woman, a Countess, is the Prince's governess. The entourage is rounded out with the Prince's valet, Georges. Nelson is taken aback; clearly he's not accustomed to dealing with children, royal or otherwise. He tries to sidetrack him with an offer of refreshment--which the prince seems happy to accept--but the Colonel angrily demands to know immediately what is going on. The Colonel deduces that there has been a revolt back home, and the Prince anxiously asks about his father. The State Department man tells him. The Prince reacts as you might expect, but I timed it--his grief lasted just over one minute before he suddenly realized that he was now the King, and no one could tell him what to do anymore. (Oddly enough, the Prince does not insist on being addressed as "Your Majesty". Until the end of the episode, they continue to call him "Your Highness".)
Nelson brings the Prince and the Colonel to his cabin. Presumably he did so in order to discuss the situation further, but if so, he completely forgot about it when the Prince commandeered the cabin for his own use. (I loved Nelson's expression.) The Prince is already throwing his weight around, and enjoying every minute of it; he hints that he will end the current friendly relations between the two countries if Nelson won't give up his quarters. Later, the Prince prepares for bed alone. Looking around nervously, he locks the door, arranges a lump under the covers in the bunk, then settles himself on the far side of the room, armed with a tiny pistol. His actions are justified. Some time later, the door is forced open and a knife thrown at the bunk. The Prince opens fire. The Colonel and Georges (presumably sharing a room) rush out into the corridor, glance around, and enter the room, quickly followed by the Countess. Nelson and Crane (probably sharing Crane's quarters) turn up in short order. The Countess's first reaction to the Prince's announcement is to note that he stole her pistol. The Prince is understandably outraged, the more so when Crane tries to brush it off as a nightmare. The knife in the bunk indicates otherwise. Crane, who is a fine submarine captain but would make a rotten policeman, simply picks the knife up with no regard for possible fingerprints. The assassination attempt leaves the Prince suspicious of everyone. The following morning, he ensconces himself on the periscope island in the middle of the Control Room. This actually puts him pretty much out of everyone's way, and the crew more or less ignores him. O'Brien notes an odd reading, which is confirmed by Sonar--something's behind them, and has been for the last hour. It might be fish--or another submarine. They alter course. Nelson enters the room, and is rather startled to find the Prince there. Nelson understands that the Prince is frightened and trying to protect himself as best he can, but Crane is aggravated at having a kid underfoot (although, as I said, he was out of the way). The Prince gets peeved at Crane (and vice versa), and Crane is a little irked at Nelson for bowing to the Prince's demands. In the nose, Crane and Nelson discuss the situation. If the assassination attempt was not faked by the Prince, then the killer must be one of his entourage--a sleeper agent. The only other possibility is that it's one of the crew. Or, as Crane points out, Crane himself. This comment breaks the tension, but moments later, Crane receives a message of a foundering ship, and is shocked when Nelson refuses to delay their mission to search for survivors.
"Silent Night" plays over the intercom, the quiet melody an odd contrast to the irritated crew in the mess hall. Their discussion is interrupted by Georges, who attempts to take over the galley to prepare the Prince's lunch. Cookie defends his turf with a cleaver, and Georges grabs for a knife inside his jacket. Prudently, he backs down. In the Control Room, Sonar is picking up the odd readings again. They have to assume that it's a submarine. The outraged Georges comes in, complaining to the Prince, who is equally outraged. Nelson's attempt to smooth things over doesn't work well; the Prince is too excited to explain properly. Crane's grumbling aside leads to the Prince demanding his arrest, which in turn leads to Crane's immortal line: "Your Highness, why don't you shut up?" (Hedison got some of the best lines in this episode.) The Prince actually does shut up, too shocked to speak. Before he can get his voice back, Sonar reports that the other sub is bearing down on them. Crane instantly switches to full command mode, ordering both Battle Stations and the Prince's removal. To their credit, the Colonel and Georges instantly hustle the Prince out of the room. The enemy sub fires on them. Crane fires back, although the firing sequence does not match his commands--he order four missiles fired one by one, but they went out two by two. The second missile hit dead on.
Somewhat humbled, the Prince actually asks permission to return to the Control Room. Nelson leaves it to Crane, who allows it. Sonar picks up a surface contact. As Crane prepares to investigate with the periscope, the Prince arrives, and reacts just like any little boy--he wants to look first. After the Prince changes his order to a request, Crane lifts him up, in one of my favorite moments of the show. (Either the kid was standing on a box below camera range, or David Hedison was a very strong man; he seemed to hold him without much effort.) The Prince spots a man on the surface. Crane looks for himself, and the man appears to spot the periscope. Crane asks if they can retrieve the castaway, and the Prince, promptly tossing his newfound courtesy out the nearest hatch, commands that the man be brought aboard, over the Colonel's protests. As the man comes aboard, the Prince shows an odd mixture of compassion and arrogance. He's concerned for the man's well-being, but demands that the crew look after him without giving them the chance to do so of their own accord. The man, with a rather Irish accent, seems only moderately startled at finding a boy in charge. His matter-of-fact, but sincere gratitude softens the Prince a bit.
As the Admiral and the Captain take a meal together, we learn that "John" has two stories to tell. Nelson was told that he was the captain of a freighter that went down (which corresponds to the distress message received earlier) but the crew was told that John was king of an island that sank when a volcano erupted. Nelson's amusement dies abruptly when Crane comments that the man is off his rocker. John, in the meantime, goes wandering off down the corridors, playing a flute, unaccompanied by any guards. He comes to the Prince's room (now guarded by Patterson). John seems quite content with his situation--good food and warm clothes; what more could a man ask? The Prince invites him in, over Patterson's objections, and tells John of his own situation. John plays him a tune (and either he was actually playing it, or finger-synched it very well). He then sings the lyrics of the tune (which was quite lovely, considering that I've only heard Carroll O'Connor warbling "Those Were The Days" as Archie Bunker). The Prince's reaction to a sudden movement by John clues John in to the fact that the Prince is a very frightened little boy. John has quite a calming effect on him, later tucking him in bed while unobtrusively giving him pointers on a king's conduct. Nelson, the Colonel, and the Countess enter the room, all concerned about John staying in the boy's cabin. The Prince starts to throw a tantrum, but is quickly settled down by John. Nelson changes his mind, allowing John to stay. It would be interesting to know if Nelson simply decided that John was not dangerous--or if he was thinking more of the useful influence John was having. Leaving the room, the Colonel is upset about leaving John there, and threatens Nelson. The Countess is more pleasant--but just as threatening.
There's some passage of time, although we're not shown how much. Presumably due to John, the Prince's presence is becoming more accepted by the crew--while the Prince is becoming more friendly to the crew, as shown by a game of gin. Approaching the harbor of the Prince's home, Sparks cannot get through on the radio--it's being jammed. The U.S. Embassy manages to get a message through. The rebel group have taken over the T.V. station, telling the populace that the U.S. had killed the king and his heir. The embassy warns them not to land. That evening, someone approaches the Prince's room. I realize that it wouldn't have looked nice for a crewman to get himself killed on a Christmas episode, but they should have done something to explain why the guard suddenly vanished from the Prince's door. This time, the killer doesn't try killing from a distance, instead coming right up to the bed. John suddenly springs up and grabs the knife. (Hard to say if John took the bunk to serve as decoy, or if the Prince's growing courtesy led him to offer his elder the bed.) The Prince's yells for help bring Nelson and Crane on the run--the guards (if they were guards, and not just random crewmen) followed afterwards, and the Prince's remaining entourage didn't show up at all, which seemed very peculiar. The would-be killer is the Countess. (They had a surprising number of women bad guys on this show.) The Prince wants her executed immediately, grabbing up the knife when the crew don't obey instantly. Nelson disarms him, and John quickly points out that a king should abide by the law of his land--or be a tyrant. Nelson requests the Prince's presence in the nose, and explains the problem to him. They need to show his people that the Prince is alive and well--but making a broadcast will expose them to attack. The Prince solomnly agrees to the broadcast, and makes quite a stirring speech. The T.V. station is quickly returned to loyal hands, and there are demonstrations everywhere for the Prince's return--but there is also a ship topside, coming after them. The Prince is terrified, but John agains calms him, commenting that he will deliver a Christmas present to the people--a king. More ships arrive, turning out to be--Tah Dah!--the U.S. 7th Fleet. Back home, the new king prepares for the ceremony of the scales. I wonder if someone unbalanced those scales, because it looked as though the Lords put in as much gold as they did for his much larger and heavier father. Nelson and Crane are on hand for the ceremony, as is John, who, after encouraging the Prince to accept his destiny, abruptly vanishes, somehow leaving his flute sitting on top of the gold. Seaview heads for home, further decked out for the holiday season by a tree presented to the crew by the new king. Crane is left wondering about their mysterious visitor, and Nelson casually points out that they picked him up in the vicinity of...Christmas Island. Conclusions may be drawn by the viewer.