Dr. Merrick faces a testing time when a terrified hospital patient claims her husband is trying to kill her, but Merton seems reluctant to get involved, while Vernon picks up a bargain all-purpose pest-control solution, enlisting David's help in his eradication mission. Gina's cousin Diane arrives to help her and Phil with the wedding preparations - much to the delight of PC Crane, who's instantly smitten.

Dennis Merton is called to Ranby Hall to investigate the sudden death of racing driver Jack Maclean from a massive insulin overdose while he was under the care of Liz Merrick and Dennis's wife, Jenny. Meanwhile Vernon bumps into an old friend who offers him a gilt-edged business opportunity which leads him into serious trouble.

A new sergeant arrives at Aidensfield police station, bringing plenty of radical ideas from his time in the city, much to the officers' disgust. When news gets out of his ambitious plans, which will leave Walker unemployed, Oscar decides to take a stand and rallies the troops.