When Scotland's leading virologist goes missing, Mona and Paterson from the Health Enforcement Team are dispatched to London to find him. In a hot and unwelcoming city, Mona has to deal with a boss who isn't speaking to her, placate the Professor's over-bearing assistant, and outwit the people who will stop at nothing to make sure the academic stays lost. Meanwhile, back in Edinburgh, Bernard is searching for a missing prostitute, while Maitland is trying to keep the Chair of the Parliamentary Virus Committee from finding out quite how untidy the HET office is.
