After having a nightmare about a legendary seafoam monster, Sackville grows increasingly afraid of falling asleep and tries to keep himself awake all night. Oromocto, Aulac and the Captain try to convince him that dreams are a normal part of sleep, and that seafoam monsters are just a myth perpetuated by some sailors.
One night aboard the HMCOCS Glacier, the entire crew is seemingly sound asleep, a calm quietness in the air, when Sackville suddenly begins to toss, turn and grunt in his sleep. He begins to have a nightmare where he is slumbering on the surface of the sea, when the waves suddenly roughen and mist up, and seafoam begins to bubble around his body in a human-like shape, lifting him into the air as if someone was picking him up from under his arms. Sackville then realizes to his horror that it's not human at all as the seafoam starts to shape itself into a grotesque figure and tie itself around him in choking knots - it's in fact a seafoam monster. He jolts himself awake from the nightmare, breathing so heavily that some of the other sailors can hear. Oromocto wakes up and asks Sackville what's the matter, to which he replies, stammering with fear, that he had a "terrible nightmare". Oromocto asks Sackville to tell him about it in the morning, and tells him to go back to sleep. However, Sackville can't sleep after that horrible dream, and he spends the rest of the night trying desperately to stay awake to avoid having it again.
The next morning, a worn-out Sackville shuffles up on deck towards Oromocto and Aulac, who are carrying out the daily cleaning duties. Oromocto asks Sackville what his nightmare was about, and Sackville rapidly fires off an explanation of the events of last night's bad dream, rambling out of terror. Oromocto and Aulac confirm that he did indeed see a seafoam monster in his nightmare, which shocks them even more. Oromocto suggests that Sackville tell the Captain about the bad dream to Aulac, who repeats this advice to Sackville. Sleepily agreeing, Sackville shuffles off towards the Captain's office, groaning to himself.
Inside the Captain's office, Sackville slumps in a chair and repeats the explanation of his bad dream he gave to Oromocto and Aulac. The mention of the seafoam monster takes the Captain a little by surprise, and he notes it down in the crew log. He tells Sackville to not get so panicky over a myth that some sailors like to recount, and says he should just try to sleep normally tonight. Sackville drones in an almost hypnotic manner that he "must try to sleep" as he drags himself back out on deck to try to help as much as his tiredness will allow with the cleaning.
That night, Sackville tries to get a good night's sleep, but he soon begins tossing and turning again, and the nightmare returns. He relives the terrifying ordeal of being pushed around by roughening, misty waves and getting tied up to the point of almost being choked by the seafoam monster. As it is about to swallow him up in thick sea scum, Sackville forcefully jolts himself awake from the bad dream, breaking out in a clammy sweat so his hair sticks to his moist forehead, shivering with terror. Oromocto wakes up and asks him if he had another nightmare, to which Sackville can only give a fearful nod as he clutches tightly onto his duvet. Oromocto reminds him of the Captain's assertion that seafoam monsters are just a myth and that he should just get back to sleep, but Sackville hides under his pillow and duvet, shuddering uncontrollably as memories of the nightmare race through his mind, keeping him awake.
The morning after, Sackville is so exhausted that he can't stand up straight, his hands dragging across the floor. He can only just barely reach Oromocto and Aulac in time for the salute. Oromocto says it's almost time for his favourite part of the day, but he then notices Sackville's hunched posture and begins to feel concern for his wellbeing as he seems to have gotten no sleep at all after that bad dream. The Captain arrives on deck and carries out the salute for all the sailors, who then follow suit. Sackville tries to copy, but all he can manage is a weak flop of his left arm up to his forehead and down again, which catches the Captain's attention. He calls out to him, and the other sailors take notice. He asks Oromocto if it's because of the nightmare he had, and Oromocto agrees.
At that moment, Sackville suddenly collapses to the floor in a heap, totally out of energy. Aulac cries his name out as he, Oromocto and the Captain rush over to attend to him, with the other sailors looking worried while they watch over. By now, Sackville has fallen into a deep sleep, and Oromocto props him up, supporting his back with his hand. Aulac laments at Sackville not being able to get any sleep at all over the past couple of nights, adding that he just isn't his usual self when he's tired. The Captain leans in and manages to convince Sackville that the seafoam monster was just a terrible nightmare, and dreams are a normal part of sleep - whether they be good or bad.
As the Captain speaks, Sackville's heavy breathing in and out begins to calm down, as if in understanding. Aulac remarks that he "finally got the message", and Oromocto praises Sackville for finally getting to sleep. The Captain stands Sackville up, sliding his arms around Oromocto's neck, who holds on to his hands. They carry him over to the dormitories so he can sleep properly, where Aulac tucks him into bed and gives him a glass of milk to aid his sleeping. The Captain says he'll make an exception for Sackville today since he's too exhausted to carry out his usual duties. Aulac tells him to have a good rest as he, Oromocto and the Captain leave, because he'll need all the energy he can amass for tomorrow.
Much later on in the night, Sackville is soundly asleep, when he starts to grunt, toss and turn as the nightmare returns for the third time in a row. He once again re-experiences the horrors of seeing the sea mist up and roughen, the water bubbling over and mutating into the much-feared seafoam monster, who goes on to tie Sackville into intricate knots. It hovers its hand above its mouth as if it is about to eat Sackville, who begins to scream as thick sea scum swallows him up. He desperately tries to wrench himself away, but his efforts are all to no avail, and he lets out a final scream as he is completely swallowed up by the sea scum, his voice distorting into bubbles. Sackville drifts helplessly towards the ocean floor, curling up into a defenceless ball in silent surrender to the merciless wrath of the seafoam monster.
Using all his strength, Sackville powerfully jolts himself awake from the nightmare, pouring out sweat, breathing so heavily that all the other sailors can hear. Oromocto wakes up, knowing that Sackville had yet another bad dream, but he reminds him about what the Captain said - seafoam monsters are just the stuff of myths and dreams are a normal part of sleep, telling him to just go back to sleep and not think about the nightmare too much. Sackville remembers that important advice, and he calmly falls asleep again, looking contented. Oromocto praises him, and he soon goes back to sleep too.
Sackville arrives on deck the next morning feeling refreshed and fully energized after having had a good night's - or rather, day's - sleep. Oromocto and Aulac see him coming just as the Captain is readying the salute, and they both notice that Sackville looks - and feels - a whole lot better now that he's had a good rest. The Captain and the other sailors also notice Sackville's regained energy and better mood, with the Captain remarking that he finally got to sleep through the night after three days of restlessness. Sackville thanks him, but the Captain then asks him if he had a nightmare, to which Sackville admits rather ashamedly that he did. The Captain reminds him of his reassurance once again - we all have dreams, and some are good while others are bad, and seafoam monsters are just an "old sailors' tale". Sackville smiles again, promising himself that he'll never think his nightmares are real ever again. Oromocto adds that they never are, unless they're made real, and the Captain and all the sailors laugh out loud together while Sackville beams brightly in the warm morning sunshine.
- This episode's rating is raised to TV-Y7 from the series' usual TV-G, due to the horror themes which may frighten children below the age of 7.