Professor Larry Fischer's beautiful 1929 Vaaxhall Hurlingham, (after which the series takes its name) is the family treasure and the pride and joy of the professor. James Marriott, Professor Larry Fischer's rival to his property, has an expensive thoroughbred horse, Auckland Star. He intends to use the horse, to earn himself some money. Deborah, Professor Cross's teenage, daughter, loves horses. James, up to some devious tricks, decides to let her take care of all his horses, including the Auckland Star. But strange things start happening when Kerry, one of the horses and Auckland's constant companion, suddenly starts behaving strangely. Pete, Deborah's brother, investigates. Kerry is an ordinary old horse, but he is the mascot and constant companion of the thoroughbred Auckland Star. Why are they suddenly behaving like strangers?

A deadly, infectious disease is plaguing the animals around, while the Marriot Research Laboratory is trying to find an antibiotic that will arrest the disease. But Dr King, the lab researcher, plans to blackmail James by threatening to spread the deadly virus. To her surprise, her uncle James Marriott gives Deb a present. But the new spirit of friendship is soon soured. Is the Fischer family responsible for a killer epidemic that would destroy New Zealand's farming industry?