The cartoon's title is a play on the phrase "sweet and sour."
Granny leaves the house for an outing, but as she drives by the house and waves goodbye to Tweety, she sees Sylvester has gotten into the house and is about to eat the bird. Granny stops the cat in time and, fed up with his constant chasing after Tweety, gives him an ultimatum: "If there's so much as one little feather harmed on the canary, it's off to the violin string factory!" (punctuating the warning by mimicking Frédéric Chopin's "The Funeral March").
As Sylvester sulks in the corner, Tweety is about to face a new threat — a rough-looking orange cat wearing an eyepatch. The unnamed orange cat is after a meal of his own and is uncaring that Sylvester will be deemed responsible if Tweety is noticed missing. As such, the chase now casts Sylvester not as the predator but as the (not-so-altrustic) protagonist who plans to save Tweety from a predatory cat before Granny returns — moreso to save his own skin. After several exchanges, with both Sylvester and the orange cat clobbering each other, Sylvester finally gets rid of the predatory cat by blowing him up in Granny's chimney (by way of a lighted TNT candle tied to a balloon).
However, Sylvester's efforts are in vain. As he is putting Tweety back in the cage, Granny enters and, assuming he was after Tweety, promises to make good on her earlier threat. "Aw, what's the use, she'll never believe me!" mopes Sylvester as he plays Chopin on his violin and falls into the violin case as a coffin to his doom.