A rich financier and owner of a baseball team adopts a spirited cat that he names Rhubarb who embodies values that he admires. When he dies he leaves his estate to the cat and names his employee and friend Eric Yeager Rhubarb's guardian. Trouble ensues when Banner's daughter disputes his last will and the baseball team threatens to quit because they get ridiculed by rival teams for being owned by an animal.
Rhubarb, who is named thus for the color of his pelt, lives on a golf course where he loves to collect golf balls that land in the bushes close to his hideout. This irritates the golfers to a degree that has one of them let loose his two dogs on the cat. After much noise and shaking of the bushes, indicating a fierce fight, the dogs turn tail and run, whining pityfully all the way. The incident is observed by T.J. Banner, who comes there often just to watch the cat go about his deeds. This time he has brought along two people he's meeting with to discuss the crappy performance of his baseball team. He uses the cat as a symbol of what society is lacking these days - too many yes-men and not enough spunk in the world - to point out what qualities his team lacks in. He ends the meeting by telling his assistant and friend, Eric Yeager, that he has to have that cat.
Having been on ill terms with his daughter for the longest time, Banner leaves his fortune and his baseball team to Rhubarb out of a general disgust for the human race and his daughter in particular when he dies. Knowing well enough that a cat cannot manage his estate, he names Yeager Rhubarb's guardian. Yeager is reluctant, outraged even, to be saddled with the job but Myra breathing venom makes up his mind for him and he declares that he will see Banner's will executed.
Trouble arises again when the baseball team makes it known that it is not happy about being ridiculed and meowed at at the stadium and threatens to go on strike by feigning injuries and ill health, or to quit. Yeager thinks it one less headache but Polly, his fiancee and daughter of the team's manager, convinces him to do something about it. Raging about those superstitious screwballs actually gives him an idea. He takes Rhubarb along with him to the next meeting of the team and observes who responds favorably to his talk about other teams and even political parties having an animal for a maskott. Those who pet the cat then suddenly recieve a cheque under the pretense that accounting made a mistake the year before. Since it hadn't been turned over to Uncle Sam they now were lucky to get a little extra money. A very young Leonard Nimoy gets his moment in the limelight jumping up and demanding to know if the cat will be at the next game. Now, all could be well if Yeager's fiancee hadn't developed a mean allergy against cats in the meantime.
From now on, when he wishes to be with Polly, Yeager has to de-cat first. Meaning he has to bath and put on fresh clothes that weren't exposed to Rhubarb in any way. Therefore, the evening he is supposed to get married, Rhubarb has to stay home. Coming back for something at the last moment, he catches Myra going after the cat. The wedding is called off, and Myra is shown the door. From then on Yeager has to travel with the team because they absolutely refuse to play without their lucky charm present and he can't let Rhubarb out of his sight.
Danger lurks next when everybody starts betting on Brooklin, the team owned by Rhubarb, to win the World Series and the bookies start loosing serious money. They hatch a plan to abduct the cat. The police is looking for him and Polly sniffs her way around the city's legal and illegal betting shops. Rhubarb is found at last but gets lost again in a car chase. Now all of Brooklin is looking for him because their team plays New York and they are determined to show them. Miraculously Rhubarb finds his way into the stadium and makes a beeline for his customary booth. He knows a game was on because the bookie on duty to guard him was watching it on TV. To Rhubarb it meant that the woman always sitting right behind them who had started to bring her cat to the games would be there. All turns out well, Brooklin wins, Rhubarb gets a litter and Polly and Eric push a pram. The End.
If you love cats, you might love this film. Oh, and yes, Leonard Nimoy is in it, too.