Edinburgh, just before Christmas. The weather forecast announces that a front of bad weather is approaching but will probably lose force over the ocean before hitting land, resulting in the wet conditions over the holidays which are so common in this country.
Not far from the city the research facility of Oxenford Bio Lab, informally known as the Kremlin, is in a permanent state of heightened security. This is where an attempt is being made to create an antivirus to the deadly Madoba 2 virus, which is as dangerous as the Ebola virus. Stanley Oxenford, who founded the company, has invested his entire fortune in this project.
By the morning of Christmas Eve a festive mood has descended on the staff of the biotechnology company, only slightly distracted by an announcement from Antonia “Toni” Gallo, head of security in the company. She wants an inventory of the entire stock to be completed before the end of the year. As for Christmas Eve, the chief executive Stanley Oxenford is a widower, and he plans to spend the holidays at the family home with his three grown-up children and their families. Toni is going to celebrate briefly with her mother and her sister's family, and then - as soon as possible – escape for a short wellness break with a girlfriend; as a single woman she prefers this kind of thing to the traditional family Christmas.
Suddenly the lab is thrust into alarm: the inventory has established that a dose of the antivirus is missing. What's more, Toni discovers that a member of staff, Michael Ross, has smuggled an infected rabbit out of the BSL4 High Security Laboratory. She and her team, equipped with protective overalls, immediately make their way to Ross's house... where they find him dying in agony. Apparently he is a secret animal conservationist and inadvertently infected himself with Madoba-2 when he was trying to save the life of the rabbit with the antivirus they have developed in the lab. This was a fatal mistake, because the antivirus is not yet refined enough to be used as medication. This incident is a huge challenge for Toni, but by using all her skills and charm she is able to persuade the police and the general public that there is no need to panic, since there is ample proof that nobody else has been infected with the virus.
Meanwhile Kit Oxenford, the son of the company founder Stanley, finds himself in a very serious trouble due to his gambling addiction. He owes £250,000 to a shady gangster called Harry Mac, who is blackmailing Kit and forcing him to steal the antivirus from his father's company. Some time ago Kit himself wrote the security program for the company, and consequently he knows exactly how to evade the security system. The gambling addiction is an old story with Kit, and several times in the past he used accounting tricks to steal money from the firm. In those days Toni Gallo was merely a security consultant for the company, but finally she worked out what he was doing. As a consequence Stanley reluctantly fired his son, so stealing the antivirus is also a way for Kit to take revenge on both his father and Toni.
On the afternoon of Christmas Day Toni comes to visit Stanley at the family home so they can watch the way the media reports the incident at Oxenford Bio Lab together. While she's here she also meets the whole family of the attractive widower, as everybody has now arrived for the festivities. Kit is naturally far from pleased to see Toni. His two sisters are also here, Olga and Miranda, with their families. It is obvious to everybody present that Stanley and Toni are very attracted to each other, although they both do their best to suppress this.
During the course of the evening Kit manages to steal his father's company security pass, which he will need in order to get into the high security area of the laboratory. And from here he uses the Internet to disable the telephone system at Oxenford Bio Lab, thus setting his ruthless plan in motion.
Although the forecast was only for rain, a snowstorm is rapidly approaching the area. Toni's plans for Christmas will have to be cancelled, since the security guards at Oxenford Bio Lab report to her that almost the entire telephone system has collapsed. Toni therefore decides to go back to the company. Meanwhile, while everybody is asleep, Kit sets off to meet Nigel, Daisy and Elton, the other members of the gang who will perform the robbery. They tell the security guards at Oxenford Bio Lab they are engineers from the telephone company who have come to repair the phone system. A short time later they force their way into the laboratory. But when he approaches the refrigerated safe containing the virus and antivirus supplies, Kit get a nasty shock: he discovers that instead of stealing the antivirus he is supposed to remove the extremely dangerous Madoba-2 virus itself. So the gang slips out of the laboratory just before Toni arrives, carrying the virus in a harmless-looking perfume atomiser... all ready for use in a terrorist attack. Toni has been delayed by the blizzard, and the gang now also finds they can't progress far in these weather conditions. They therefore resolve - much against Kit's will - that they will go to the Oxenford family home and wait for the weather to improve.