The highly incompetent Digby and his ever-faithful secretary Thelma find their 9-5 `domestic' harmony threatened when a new manager arrives - who looks like sweeping them clean out of Rid-o-Rat and straight into the nearest labour exchange.

Can Thelma and Digby stem the tide of the super rats? And what sort of rat wears a green ballet dress or is called Kes?

Rid-O-Rat is about to launch a sensational new pesticide. Thanks to Digby, the secret formula suddenly vanishes. Thelma turns safebreaker extraordinaire to save the situation.