DS Ed McCusker, portrayed by Connor Swindells, is a young Scottish police officer who works alongside DCS John Orr and other officers to manage the chaotic aftermath of the Pan Am 103 bombing, helping to gather evidence and hold the investigation together on the ground in Scotland.

In Episode 1, the investigation begins with the grim task of determining whether the crash was an accident or a deliberate act. DCS John Orr solemnly declares it 'an act of war' and leads the team in searching for evidence to confirm if a bomb caused the explosion on Pan Am Flight 103.

The first episode introduces several key investigators including DCS John Orr (Peter Mullan), DS Ed McCusker (Connor Swindells), and FBI Special Agent Dick Marquise (Patrick J. Adams), who represent the Scottish police and American authorities collaborating on the case.

Episode 1 shows the devastating physical aftermath of the Boeing 747 breaking up over Lockerbie, with debris scattered over an 850-square mile area, and portrays the emotional toll on the local community and families as they confront the tragedy and search for their loved ones.

The investigation scenes in Episode 1 primarily take place in Scotland, focusing on the crash site near Lockerbie, where the Scottish police conduct their initial search and evidence gathering. The series also sets the stage for the broader international investigation involving the US and Malta, which unfolds in later episodes.