(NOTE: I thought I'd be the only one writing what I did below, but I see the others here agree. I guess it was pretty obvious - this was overdoing the bait-the-cat bit. Anyway, here is what I had written:)
The owners have left on vacation for two weeks - a trip to California - leaving the cat (Sylvester) all alone and locked in the house. That means no milk, but the cat, to his relief, does find a bunch of canned tuna. However, to his dismay, he can't find the opener.
It turns out the little mouse in the house has it...and baits the cat with it. This is a mean rodent who keeps teasing Sylvester with the opener and then yanking it away at the last second. Sylvester tries everything possible to open the can of tuna but can't do it.
This is a frustrating story, and why they make the sadistic mouse the "good guy" is beyond me. It's like some of the Tom & Jerry cartoons where poor Tom always gets the worst of it even though many times the little mouse starts the conflict!