When a nasty stomach bug sweeps through Portwenn, Martin takes to the radio to alert residents to the danger.
A new police officer, who has narcolepsy, replaces Mark Mylow, and Martin treats a girl who's been taking her mother's diet pills.
Louisa's ex returns to Portwenn hoping for a reunion, and Martin sees a patient who has a history of self-injury.
Martin's house call to the Flint brothers leads to a diagnosis of food poisoning, and Al learns that Bert is not his natural father.
Martin prepares to leave Portwenn when his relationship with Louisa fails.