They are not like other rats. They work at night, in secret . . .
Time is running out for Mrs Frisby, a widowed mouse with four small children. She must move her family before the farmer destroys their home. But her youngest son, Timothy, lies ill with pneumonia and is too sick to be taken on such a perilous journey.

Help comes in the unexpected form of a highly extraordinary breed of super-intelligent rats. The rats of NIMH come up with a brilliant solution to Mrs Frisby's problem but the rats are in danger too, and little by little Mrs Frisby discovers their extraordinary past . . .