A massive unexploded bomb is found in Scotland. Interpol race against time to find anyone who may know something about the construction of the bomb so an attempt can be made to disarm it.
An unexploded bomb is discovered beneath a Scottish dam, with heavy rain raising the water level behind it by the hour. Interpol are called in to help trace those responsible for its design, members of a secret German research group. Duval finds that the only man who can help has his own reasons for not wanting to be found.