1) The Fourth Horseman

The episode opens at Abby Grant's rather large and luxurious house in a village to the west of London. The first we hear of The Sickness is when her son, Peter, phones from boarding school to reassure her he's OK - Abby and her housekeeper discuss what they think is a flu bug going around.

Abby drives to Brimpsfield station to pick up her husband, David. The rail system is in chaos due to staff shortages and power failures. The car radio tells of traffic chaos around London, and similar problems around the world. Half of the workforce is off ill.

Abby decides to wait at the station until her husband arrives back from his job in London. He doesn't arrive for hours, and has heard rumours about millions of deaths in China from a mysterious disease. Neither of them think it can happen here...

Our first encounter with Jenny Richards is as she nurses her sick flatmate in London. She decides to go in search of her flatmate's boyfriend, Andrew, who is a doctor at the nearby hospital. When she arrives, the hospital is full and there are long queues of people waiting for flu vaccinations.

She finds Andrew, who tells her that the authorities are aware that the epidemic is not flu, and the vaccinations are just to avoid panic. He tells her that there have been many deaths in the hospital already, but they are being played down. The disease takes six days from initial infection to reach its crisis point, and only one person in the entire hospital has survived past this crisis point. Sufferers have lumps under the armpits and a very high temperature, although they feel very cold.

By the time they reach Jenny's flat, her flatmate is dead. Andrew admits that he too is ill, and tells Jenny to flee the city - law and order have collapsed and secondary disease is spreading. She sets off on foot and is accosted by a group of looters. She manages to escape and thereafter avoids everyone she sees.

Meanwhile, Abby has caught the disease. She awakes four days later to find the corpse of her husband lying on the sofa, and everyone else in the village dead. She sets off to drive to her son's school.

By now Jenny is out in the countryside. She meets a Welshman, sleeping rough, who won't let her come near (he turns up again in later episodes). By now she is desperately lonely. She hears Abby's car, but is too late in reaching the road to allow Abby to see her.

Abby reaches the school and finds Peter's bed in the dormitory empty - many of the others contain dead bodies. There is a single survivor at the school, an aging teacher. He tells Abby that Peter was in a group of (as then) unaffected boys who went off to camp in an attempt to avoid the epidemic.

Abby returns to her house, takes what she needs, cuts her hair short, then douses the house with petrol. In the final scene she stops her car on a hillside, and looks down at her burning house. She seems to have aged about ten years since the first scene!