After stunning Captain Britain with ray blasts, undersea robots net their captive and drag him inside the mechanical monster of Loch Ness. The numb superhero is hauled through an airlock in the monster’s metal belly and up a ladder to the control room, where a huge alien being with a grotesquely misshapen head awaits. He announces that he must question the only earthling bold and powerful enough to uncover their secret outpost on this doomed planet. Brain-waves pulse from the alien and stir Captain Britain out of his daze.
(The alien’s tale)
The creature explains that he belongs to a race with great energy needs. For eons, they scouted the universe for new sources of energy. While on a space probe, he discovered Sol. He decided that it would take centuries for the equipment to arrive to harness this sun’s energy. Until then, he’d hide on Earth to see if that planet would threaten his race’s purpose. The ship descended into the murky waters of Loch Ness and the alien concealed it with a hull resembling a prehistoric undersea monster. The alien watched humanity progress and saw them build new machines and weapons during World War II. From time to time, his craft was sighted by Earthmen. But its guise frightened them into doubting their own eyes.
Finally, humanity was able to fire rockets to probe space and reach the moon. The alien decided that mankind had progressed too far and had to be stopped… for even now mankind is tapping the solar energy, which the aliens claim for their own. Thus, the alien announces, he intends to build satellites that drain Earth of all its power. Homes and buildings will grow cold, with no means to heat them. Civilization will no longer function and mankind will perish.
Captain Britain alone may survive, the alien offers, if he tells him the source of his sceptre’s mystic energy and gives him the weapon. Never, Cap shoots back. The star sceptre was not meant to be used by the ruthless and cruel!
The alien orders its robots to attack and they proceed to do so with their ray guns. Captain Britain dodges the first blast with lightning speed and seizes one of the robots and hides behind it. He hopes that he’s guessed right about their programming. Cap holds his captive like a shield, while the other robots fire a second blast. The hits automatically trigger the hit robot’s own guns. And thus, the attack turns into a battle among the robots.
The moment’s respite gives Captain Britain time to arm himself, by willing his star sceptre to become a longer fighting staff. Like a vengeful whirlwind, he swings it about him, felling the robots. Staff before him, he leaps at the alien, but he crashes head-on into an electrified force-field, which hurls him back, writhing in agony.
Meanwhile, at Lochside, Courtney and Jacko are examining the bathysphere and the site where the equipment was stored. Jacko finds that the bathysphere’s cable was clearly cut and, in the storage shed, Courtney a button. None of the crew has lost a button, so it has to be from someone who had no business being there. Jacko sees the innkeeper and notices that a button has been torn from his vest.
Below the surface, the alien is about to seize Captain Britain’s star sceptre. The injured Captain concentrates and manages to create an invisible barrier between himself and the alien.
On the surface, hotheaded Jacko grabs the innkeeper, ordering him to confess that he cut the winch cable.
In the sub, Captain Britain darts from his foe and finds the master control panel blocking his way. He intends to damage it but, suddenly, demonic creatures appear before the speeding superhero. Without a second thought, Cap rips loose a guardrail and finds that his weapon passes through them. They were but specters, conjured up by the alien. Nothing more stands between him and the panel, and he proceeds to destroy the it.
Above, McNab jumps into the loch, rather than let himself be caught.
Even as the alien warns Cap of the powers he’s unleashing, a series of explosions shakes the sub. As one of the blasts ruptures the ship, Captain Britain seizes his last chance at escape and flies upward. One final explosion resounds from below, blowing to smithereens all trace of alien and craft. In the following maelstrom, McNab drowns.
Later, Brian joins the other students, making an excuse about taking a walk before daybreak and falling asleep in the heather. Courtney tells him the investigation was a waste of time. There’s no proof of the Loch Ness monster. The explosion probably was some detonation equipment left over from a previous expedition. As the disappointed students leave, behind them the real monster of Loch Ness briefly raises it head.