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MacDougall..................Torin Thatcher
Lester......................Hedley Mattingly
Angus.......................George Mitchell
Andrews.....................John McLiam
Magistrate..................Joe Higgins
Crofter.....................Tudor Owen

You know, this is beginning to sound like a cloak and dagger operation.--Lee Crane

In Scotland, a man staggers into a tavern, talking wildly about a monster in the loch; he says that the doctor is still out there and needs help, but the men in the bar know neither him nor any doctor. The man goes on, saying that the others are dead but the doctor may still be alive. The men accompany him to the shore through a thick fog; the doctor, as it turns out, is dead after all. The men ask the stranger again who he is; he replies that he can't tell them, and as they continue to question him, they look out into the loch to see two glowing eyes approaching.

The Seaview is at sea. Crane looks at a map showing their destination--Loch Ness. Crane says that it will be quite a trick, since there's no way to reach the loch from the sea. Nelson replies that they aren't even going to try--he and Crane will be going ashore alone. He asks what Crane knows about Loch Ness; Crane says he's familiar with the legend. Nelson tells him that there is a secret lab 700 feet under the loch, no more than a dozen people know about it; the scientists there are working on a special project that could turn out to be the ultimate weapon. He asks if Crane has ever heard of Austin Carruthers. Crane recalls that he is a physicist. Nelson says that he's there, and has asked Nelson to do some work for him--they are to meet him and give him the results in person. He gives Crane the directions to the meeting place; if anything happens to Nelson before they meet Carruthers, he is to destroy the papers. They're to put on civilian clothes and leave the ship in an hour.

Once on shore, Nelson and Crane go immediately to the appointed meeting place, a secluded spot in the middle of the woods. A man approaches--the same man who survived the monster's earlier attack. He introduces himself as Alistair MacDougall, a professor of marine biology, and gives them the bad news about Carruthers and the other scientists. MacDougall is on his way to an inquiry about the deaths; he says he has no choice but to go, but will tell the local officials no more than they want them to know. Nelson and Crane exchange a glance and follow MacDougall to town. The three men move on; MacDougall asks Nelson to give the papers to him so that he, at least, can continue the work. Nelson apologizes, saying that he doesn't have them with him. MacDougall, disappointed, says that without those papers Carruthers' work will die with him. Nelson says that he won't let that happen--when MacDougall comes aboard Seaview he will deliver the papers to him personally. MacDougall says that it will have to be after the inquiry. Nelson suggests that he and Crane come along; MacDougall tries to dissuade them, but Nelson insists, saying that he and Crane will play the parts of newspaper reporters. MacDougall agrees, and says he'll show them the way there. Just then he sees something, and pushes Nelson aside, shouting "Look out!" They fire, but MacDougall tells them to stop, and a man comes out of the woods, hands in air; "So it was people I saw!" says the man, who claims to have been hunting a stag. Crane asks if he always hunts at night with a bow and arrow, and MacDougall says that the man must be a poacher. The three men go on, and the poacher pulls his arrow from a tree, looking after them.

At the inquiry, the crowd is hushed by the magistrate. No one believes MacDougall's monster story, although he describes the creature in some detail. The magistrate wonders what he was doing at the loch so late at night, and asks who Carruthers was. MacDougall replies that he isn't at liberty to divulge that information. Just then, a man enters the room, identifying himself to the magistrate as Inspector Lester from London and giving him a message. When the magistrate protests, Lester tells him to address his protest to the Home Secretary himself and mark it confidential; the magistrate backs down and declares the inquiry adjourned. MacDougall goes to Nelson and Crane, pronouncing it a near thing. Nelson tells him where to go to be picked up and taken to the Seaview; he thanks him for saving his life and hopes to be able to repay him someday. MacDougall reenters the building, and as Crane and Nelson pause in front of the door, the "poacher" aims his arrow in their direction and pulls his bow. As he prepares to shoot, an mysterious form strikes him on the neck, knocking him out. Nelson and Crane, unaware, move along as the hidden man watches.

Later, on the Seaview, MacDougall talks to Nelson while Crane paces. He laughs at the notion of a sea monster, calling it fascinating but not half as important as the work that lies ahead. Nelson asks what in fact did kill Carruthers; MacDougall says that's for the authorities to say--he came to get Nelson's papers in order to continue the research. Nelson replies that he has since received new orders from Washington--the papers are to remain in his safe until the cause of Carruthers' death is determined. MacDougall shakes his head, saying that Nelson's government is as cautious as his own--if they must know, it wasSeaview could reach it. Just then, Nelson receives a private call and goes to his cabin, telling Crane to get out the Scotch for the Professor. Crane does so, asking MacDougall if he likes it straight; "And what would you mix it with--seawater?" replies the smiling MacDougall

In the observation nose, Crane and MacDougall are looking at charts; Crane is about to put away the bottle of Scotch when MacDougall stops him, and Crane pours him another drink. Nelson enters, apologizes for the delay, and asks how MacDougall likes the Scotch. They discuss the entrance to the loch; Nelson says that the only proof of the monster's existence that they'll accept is to see it themselves, and asks Crane if they can be ready that night.

Later, the Seaview dives. Nelson, Crane and MacDougall are looking at charts in the control room. Sonar detects the cavern entrance, and the Seaview enters. They continue on until they reach a dead end. Nelson and Crane are called to the radio shack, and go; MacDougall looks at his watch.

On the surface of the loch, a motorboat moves slowly; three men, including Lester, are aboard. He calls the Seaview and tells Nelson that the prisoner told him everything. They know how Carruthers was killed, and the Seaview and its crew are in mortal danger. Just then something appears behind them--it's the monster. Lester shoots at it to no avail--the small boat explodes.

Crane and Nelson return to the control room. Crane wonders if they should think about turning back, but Nelson says not just yet. The sonar man detects more water below; MacDougall says that it must mean that the tunnel descends; Nelson says to try it, and MacDougall smiles. They go down, slowly and carefully. "How's that for my faith?" says MacDougall; "Your faith seems almost akin to knowledge," replies Nelson. MacDougall says that this calls for a wee dram more of Nelson's Scotch, and returns to the observation nose.

In the nose, MacDougall pours himself a drink. He looks at the Seaview blueprints hanging on the wall, examining them closely. He leaves; we see a hand open an inspection panel. It plants an explosive, which soon goes off.

An alarm goes off in the control room. It looks like a line short in the torpedo launching system. Crane tells Morton to see what's going on. He wonders where MacDougall is, and Nelson leaves, finding MacDougall in the observation nose where he offers Nelson a drink. Nelson declines, calls Morton and asks how bad it is. No one was hurt. MacDougall asks if there's been trouble. Crane announces that they are entering the loch; MacDougall says that the bay is 6 miles south--that's where they'll find the monster. Nelson tells Crane to set the course and then join them.

Kowalski is working on repairing the damage. Morton asks how it's going, but Kowalski says he's had no luck, and the duty electrician says it may take four hours to get the torpedoes working. Crane arrives and asks what caused the fire; Kowalski gives a reasonable explanation--but it's a real fluke, and could never happen again in a million years. "Unless it was done on purpose," says Crane. Morton says that that would require a lot of knowledge about the sub's electrical system. Crane nods, and asks Kowalski if he thinks it was an accident. Kowalski doesn't see how it could be anything else. Nelson calls Crane to the observation nose; Crane sends Morton to take the con and leaves.

Crane and MacDougall are looking out into the loch. There isn't much going on, but sonar soon picks up something in motion about 600 feet ahead. "The monster!" says MacDougall. He seems anxious. As they near it, it's apparent that it's no dinosaur--it looks much more like a submarine. "So that's our monster," says Nelson. "At least it's a species we can talk to." He picks up the radio, but MacDougall takes it from him, saying that maybe it's not his turn to talk yet. Nelson asks what he means, and MacDougall tells him to wait and see. Sparks announces a message coming through, and Nelson tells him to pipe it in. The voice of the "monster" tells the Seaview to stay put or they'll torpedo them, and tells MacDougall to signal them as arranged. MacDougall asks Nelson's permission to use the radio; Crane asks why they should let him, and MacDougall replies that if they don't the sub will fire its torpedoes in sixty seconds. He takes the radio and tells his comrades to hold their fire--they can't harm them since he damaged their forward torpedo section. The voice says that MacDougall is in command. Crane, angry says that MacDougall is as much a professor as he is a Scotsman! MacDougall calmly replies that the real MacDougall is at the bottom of the loch, along with the other scientists from the lab. Nelson supposes that he plans for the Seaview's crew to join them; MacDougall gloats about their ingenious use of the "monster" to spy on the lab. Crane asks what he expects--surrender of the Seaview? MacDougall says no, all they want is the plans in Nelson's safe, then they'll be free to go. "And you'll blow us out of the water!" adds Crane. Yes, says MacDougall, and if he leaves they'll torpedo him. He calls the enemy sub again, and is told to tell Nelson and Crane the terms: MacDougall and Nelson, along with the plans, are to take a minisub. If they aren't on their way in 6 minutes, they'll destroy the Seaview. Nelson watches the clock.

"Well, professor, it seems I'm in trouble," says Nelson. MacDougall agrees. Nelson wonders how he can be sure they won't torpedo the Seaview after he leaves. The voice says that he can't be sure, but he has their word. Thinking that Nelson may decide to sacrifice himself rather than release the plans, MacDougall talks about the crewmen and their families; Crane pleads with Nelson not to let them bluff him out of the plans--they'll kill him anyway. Nelson replies that he's thinking about the men. They have two minutes left. Nelson says to break out a minisub. Crane is horrified. MacDougall calls the sub to tell them they're on their way, and is given three more minutes. Crane insists that Nelson can't do this; Nelson orders him to stay right where he is and not to countermand any orders. Nelson and MacDougall leave, and Crane looks out the window at the sub.

Nelson and MacDougall go to Nelson's quarters to get the plans. Nelson opens the safe as MacDougall watches anxiously. He hands MacDougall the papers, asking if he isn't going to check them for accuracy. Irritated, MacDougall turns to examine them, and Nelson slips out of the room, locking the door from the outside. He immediately radios the missile room, saying that there's been one slight change in plan. Meanwhile, MacDougall is banging on the door--they must get off the Seaview before the time is up! Nelson hangs up the radio and lets MacDougall out.

In the observation nose, Crane stares out the window. He calls Morton, who says that the minisub is leaving. He watches it approach the "monster," and looks at the clock. He turns as he hears MacDougall and Nelson enter. MacDougall is panicky, and reveals that as soon as the minisub turns toward the sub they'll shoot. "I thought so!" says Nelson. MacDougall says that the plan was to capture Nelson and destroy the Seaview. Now they'll all die. Not if MacDougall stops them, says Nelson--he hands him the radio and directs him to ask for another arrangement. MacDougall makes the call, asking them to hold their fire for...he pauses, looking to Nelson, who says to make it thirty seconds. They agree, and MacDougall asks why Nelson asked for only thirty seconds. "See for yourself," says Nelson, and motions toward the window. The minisub is unmanned--one might call it a guided missile. It approaches the "monster" and explodes, destroying the enemy craft. MacDougall covers his face with his hands.

The Seaview leaves Loch Ness. Nelson asks if Crane thinks there's a monster; Crane says that you couldn't prove it by him. Nelson replies that one of these days, they may return to the loch and find out!