In a cozy mouse hole beneath 221B Baker Street, a brilliant detective mouse named Basil lives. When a kind toymaker mouse named Hiram is kidnapped, his brave daughter Olivia turns to Basil for help. Together with his loyal friend and assistant, Dr. Dawson, Basil faces his greatest enemy, the criminal mastermind Professor Ratigan. They race through the sewers and streets of London in a thrilling adventure of clever deductions, daring escapes, and the power of using one's wits.