Trude Mostue has worked in Bristol ever since her graduation, and now it's her last day before she moves on to her new job, which involves treating the animals at Longleat Safari Park. In King's Lynn Craig Beck deals with an emergency: Katherine and Philip Ward have adopted a stray cat called Thomas who's having trouble breathing. Craig thinks Thomas may have feline Aids and might have infected the couple's pet cat Smokey. Meanwhile, Craig's wife Alison faces up to a challenge at RAF Marham, where the ferocious guard dogs are due for their annual check-up.