Set on a small island, Sylvester lives in a lighthouse alongside his Scottish-accented master and the keeper's parrot, Polly. Unfortunately, a mouse also lives in the lighthouse, who is unable to sleep due to the lighthouse light shining into his mousehole, and constantly unplugs it. One night, the mouse turns off the light, causing a cargo carrier called Australia to run aground, resulting in a crate containing Hippety bound for the zoo to fall off. Under pressure from the lighthouse keeper to keep that "crrrrazy moose" from turning the light off again or get beaten to the pulp, Sylvester does his best to catch the mouse (while telling Polly to count the seconds till he does). Unfortunately, when he catches sight of Hippety, he starts to think he's seeing things, believing the mouse has grown giant. Things get tougher when Hippety and the mouse team up to drive Sylvester crazy, and make sure the lighthouse light stays out for good.
Tropes out! Tropes out!:
- On CBS and ABC airings, the part where Sylvester catches the mouse in an elevator and the elevator door opens and closes, alternately showing Sylvester beating up the mouse and Hippety Hoppernote beating up Sylvester was cut.
- On Nickelodeon airings, the part where the mouse uses a pair of household scissors to cut the electric wire was replaced with a repeat shot of Polly squawking, "Light's out! Light's out!"
- On The WB network, two different scenes were cut:
- The scene where Sylvester runs into the bathroom and ingests pills to fix his supposedly faulty eyesight.
- The scene where Sylvester grabs the severed wires and gets electrocuted.
- Brick Joke: Sylvester tells Polly to count the seconds as he goes to deal with the mouse. Every time he comes back down defeated, the parrot is still counting, which soon gets to the high hundreds, and then the ten thousands.
- Gory Discretion Shot: After the cord to the light is destroyed beyond repair, the audience is spared the sight of the lighthouse keeper beating poor Sylvester helpless, instead seeing the outside of the lighthouse when visual signs of the pummeling.
- Harmless Electrocution: When the mouse cuts the cord, Sylvester tries to pull it together and gets shocked, which closes the circuit and turns the light on again. At the end, the lighthouse keeper forces Sylvester to be the light by hooking him up to a car battery, turning his eyes into floodlights.Sylvester: I never thought just being a pussycat could be so complicated.
- I'm a Doctor, Not a Placeholder: In the second-to-last scene, while Sylvester is fixing the cable with tape, he angrily mutters that he's a cat, not an electrician.
- Light and Mirrors Puzzle: An accidental version is what keeps the mouse awake, despite its mousehole being at the bottom of the tower. Light leaking from the floor is reflected off a mirror and onto the path of a clock's pendulum. Whenever the pendulum hits the light, it refracts it straight into the mouse's home.
- Non Sequitur, *Thud*: Every time Sylvester runs past Polly, he tells him to keep counting the seconds it takes him to catch the mouse. After a thorough pummeling from Hippety results in Sylvester falling down the stairs, a dazed Sylvester stumbles back upstairs while telling Polly (whose counting has by now reached the ten thousands), "Keep counting, buster, I'll have that mouse quicker than you can count up to Jack Robinson..."
- Oh, Crap!:
- Sylvester has set a mouse trap and it snaps, but as he pulls it to face his victim, it turns out to be Hippety's tail. As he scans up to the "giant mouse"s face, Sylvester's expression changes from one of triumph to sheer horror.
- He has the same reaction when he notices that the mouse has wrapped a lit stick of dynamite in the cord so that when it explodes, the cord will be destroyed beyond repair.
- Oh, No... Not Again!: This is the lighthouse keeper's reaction when he learns "that crazy moose" turned off the light again.
- Polly Wants a Microphone: Polly is fully capable of talking. His usual Catchphrase is "Lights out! Lights out!".
- Violent Glaswegian: The lighthouse keeper has a thick Scottish brogue and gets quite violent with Sylvester.