A woman named Gemma is admitted to the ED showing signs of an opiate overdose and a puncture wound on her left arm, but her daughter Sheena points out that she is left-handed. Harry initially suspects that Gemma's family are responsible, but a colleague of Gemma's GP, Mark Ellis, alleges that Mark has been deliberately killing his patients for his own pleasure. Mark proclaims his innocence, but Harry investigates the claims and finds that an alarming number of Mark's patients died of an opiate overdose. After Gemma dies, and Mark admits to killing patients, Harry has him arrested.
Selena offers to submit a sample of Nathan's blood for a HIV test, but Nathan makes it clear that he is not interested and suggests that he is content with potentially dying of AIDS. Selena immediately rebukes him and assumes him that she cares, prompting Nathan to agree to be tested. When the result arrives, Nathan is relieved to learn that the test came back negative and later admits his feelings for Selena; the two share a kiss.
Paramedic duo Dixie and Cyd join the Holby Ambulance Service following a trust merger, but Josh quickly takes issue with their lax attitude towards security and using the emergency department as a pit stop. The two feel vindicated when the ambulance service's strict policies surrounding morphine results in a patient with cystic fibrosis remaining in discomfort for a long period, but Josh is unmoved and decides to split the pair up.
After Ellen announces that she has bought decaffeinated coffee for the staff room, Kelsey decides to get back at her by giving her normal coffee, but Alice accidentally drinks it and suffers a reaction to the caffeine. Alice confronts Kelsey about the rumours of her sleeping with Guppy, and Kelsey denies them; Alice is relieved and is happy to be friends with her again. Meanwhile, in cubicles, Maggie treats a police officer named Martin and cannot find anything medically wrong with him, but Tess realises that he is struggling with anxiety.
- Simon MacCorkindale as Harry Harper
- Jane Hazlegrove as Kathleen "Dixie" Dixon
- Joanne King as Cynthia "Cyd" Pyke
- Elizabeth Carling as Selena Donovan
- Ben Price as Nathan Spencer
- Suzanne Packer as Tess Bateman
- Susan Cookson as Maggie Coldwell
- Janine Mellor as Kelsey Phillips
- Georgina Bouzova as Ellen Zitek
- Luke Bailey as Sam Bateman
- Sam Grey as Alice Chantrey
- Kip Gamblin as Greg Fallon
- Stephen Moyer as Mark Ellis
- Steve Garti as Brian Sheppey
- Stephanie Dooley as Sheena Sheppey
- Andrew Turner as Sean Sheppey
- Joanna Phillips-Lane as June Welsley
- Tony Caunter as Tom Stopes
- Helen Cotterill as Felicity Stopes
- Louise Kempton as Jackie Stopes
- Robyn Kerr as Kayla Carson
- Mike Goodall as registration official
- Andrew McNair as Andrew Benson
- Stephen Burrell as Martin Worthington