Tom pretends to have a cold in order to trick Mammy into letting him stay inside for the night. Jerry tricks Tom by making him think he really is sick - with the measles.
Jasper is given an ultimatum by his master: break one more thing and you're out. Rodent Jerry does his best to make sure that his tormentor "gets the boot".
The couple that owns Tom and Spike decides they can't afford to keep both. They agree that the first one to catch the mouse can stay - bad news for Jerry.
Jerry agrees to help an escaped circus lion, whose first need is food. But first they'll have to evade Tom, who heard the news bulletin and is armed with a shotgun.