The team fear a killer is on the loose when a labourer known as "Dirty Len" dies of strychnine poisoning. A tragic chain of events are set in motion when Ventress establishes a connection to another suspicious death that took place on the same farm years previously. Meanwhile, David is led on a wild goose chase by his lurcher Alfred when he provides transport for a party of pensioner's day out in Whitby, whilst a local vet becomes caught in the middle of Jenny and Merton's rocky relationship.