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

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.

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...

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.

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.