Another deadly explosion occurs. Sarah and McKinven's growing attachment has consequences, as Kathy suspects Jean the Dean of having a secret to hide.

Two suspects derail the investigation as McKinven and Sarah are consumed by their feelings. Kathy's inability to communicate becomes a serious problem.

A second explosion puts pressure on McKinven and Sarah to find and stop the bomber. As Phil's murder trial continues, both Daniel and Emma are feeling the strain.

The task facing McKinven is more daunting than ever, especially now that his wife Azra is joining the investigation. Meanwhile, Kathy's PhD student sees more than she should...

Sarah works with McKinven to prevent another explosion before making decisions about their future. Kathy realises change is essential, personally and professionally.

Emma Hedges' return to Dundee brings her mother's unsolved murder into sharp focus, but a fatal fire in a nightclub proves an ominous omen.

Glad of McKinven's help, Emma soon feels overwhelmed by the police interest and wonders what she's started. But when the stars align to put Daniel in her path, Emma feels a deep connection.

McKinven's initial enquiries ruffle feathers and a furious Julie chides Emma for dragging up the past. When Skye threatens Emma with a knife, it's clear that someone's hiding something.

Emma is now training as a forensic chemist - and on the cusp of seeing her mother's murder case finally solved, while Daniel has returned to Dundee to give evidence against Phil.

Daniel's facing a culpable homicide charge for the Secrets fire and wants to protect Phil's reputation. But when Emma meets Phil for the first time, her instinct tells her to be wary of him.

Emma's accusation against Phil drives a wedge between her and Daniel. McKinven urges Emma to stop sleuthing, as he becomes certain that the person who killed her mother is known to her.

While Kathy oversees the excavation of Marie's grave, Daniel gives McKinven the lead he needs to make an arrest. But it's the exacting forensic science that finally brings peace for Emma.