Steed investigates an atomic plant which appears to be causing mechanical failure within a 2 mile radius.

The sisters catch a large mouse and put it in a bag as Steed arrives to visit them, claiming to be an "inspector of the National Distrust" and inspects the place.

Steed meets with the operator of the atomic plant who mentions that he believes the sisters to be the daughters of a late nuclear scientist of considerable renown.

Steed revisits and battles with an assailant outside the mill and discovers the body of the atomic plant operator.

Steed detects that it has been drugged, pours it behind his back and pretends to be knocked out, and then departs when the woman leaves the room.