© ITV/Mark Bourdillon

Bernard King, the owner of Finchmere Airfield, is hit on the head and dropped 400ft from a small plane into a reservoir, killing him on impact. Barnaby and Nelson investigate as stunt pilots Alex Darnley and Gavin Hopkirk practice daring moves for the forthcoming air show.


Alex, an RAF pilot, is the grandson of World War Two flying ace Molly Darnley and his father Perry was Bernard's business partner. According to Bernard's widow Stephanie, who has OCD, the men argued. Barnaby is thrilled to meet Molly, but Perry's wife Miranda is jealous.


The wrench used to hit Bernard is found in a toolbar belonging to veteran mechanic Duggie Wingate. Duggie recently lost his job but he denies killing his old boss, instead claiming Molly is a murderer. He accuses her of sending his sister Ellie on a wartime mission in a damaged plane, causing her death and enabling Molly to marry Henry Darnley. Duggie warns Gavin, his nephew, that he could lose receptionist Jessie to Alex in the same way.


Nelson discovers Finchmere was being taken to court over noise levels by a local residents' action group led by Jessie's father Eddie Rayner. Eddie is bitter about Jessie's plans to marry Alex, because he blames the Darnley family for his wife's death from an aneurysm.


Kate's parents, newly-retired surgeon Giles and wife Laura, arrive to visit the air show, while Miranda puts pressure on Stephanie to continue the restructuring programme. Nelson discovers the Darnleys were applying to get industrial use for the site in order to sell it at profit - the family have money problems because Perry was fired from his job with an airline.


Barnaby suspects Eddie was sending hate mail to Bernard and they go to question him. But they're too late - as Eddie waits to meet someone a small propeller plane is driven straight at his head. Gavin and Perry both admit being airborne at the time, then Barnaby triggers a family outburst by mentioning the plans to sell the airfield in front of an incredulous Molly.


Duggie visits Molly and orders her to use her speech at the air show to tell how she betrayed Ellie. Meanwhile, Eddie's logs reveal regular night flights at Finchmere using planes with no lights - is someone involved in smuggling and were Bernard and Eddie killed because they found out? Meanwhile, the hate emails are traced back to Miranda.


It's the day of the air show and, as the vintage planes swoop overhead, Miranda accuses Stephanie of going back on her word to sell up. As Alex and Gavin prepare for their stunt show, they decide to swap planes and have a side bet. If Alex wins, he also wins Jessie. But the midst of the acrobatics, Gavin's engine cuts out and Alex drops out of the sky. He somehow manages to land but the fuel line has been cut - was someone trying to kill Gavin?


Molly reveals the truth about Ellie's fateful wartime flight then the detectives go to the airfield to await the next illicit night plane. But instead of an aircraft arriving, they discover someone is smuggling goods out of Finchmere. As Alex faces a court martial and ruined career, Barnaby realises why Gavin and the murder victims were targeted. They scramble to Finchmere where the killer is waiting&ldots;