As the spring sun thaws the frozen ground, Mrs. Frisby plans to move her family out of their cozy, winter home before the farmer comes to plow and plant. The recently widowed mouse and her children—Teresa, Martin, Cynthia and Timothy—look forward to plentiful food and long, warm days in their summer home by the brook.
However, before the family can move, Timothy gets sick. Mrs. Frisby rushes to visit her late husband’s friend, Mr. Ages. The wise old mouse gives Mrs. Frisby medicine and warns her that chilly, spring nights in the summer home would almost certainly result in Timothy’s death. He must stay in the home the mice made in a cinderblock in the farmer’s garden for an additional three weeks.
On her way home, Mrs. Frisby spots Jeremy, the crow, whose foot is tangled and tethered to a fence with a piece of shiny string. With the cat, Dragon, prowling the barnyard, helping Jeremy is risky. However, Mrs. Frisby quickly chews through the string and jumps onto his back. Jeremy leaps into the air, narrowly escaping the angry cat.
In exchange for her kindness, Jeremy takes Mrs. Frisby to the owl, the wise-but-scary predator who advises the birds. And once the owl hears that she is the widow of Jonathan Frisby, he gives Mrs. Frisby his advice: “You must go to the rats.”
Mrs. Frisby has never had anything to do with the rats, but she cautiously makes her way to their domain—in the center of the barnyard’s large rose bush. Once inside, Mrs. Frisby realizes that these are no ordinary rats.
The tunnels and rooms of the rats’ home are bizarrely lit with electric lights and furnished with carpet, just like in the human world. Something very, very strange is going on. But Mrs. Frisby realizes that, while the rats may be strange, she must seek their help if she hopes to save her son.