It is the Second World War and the Royal Air Force attacks German V-1 flying bomb installations during the early summer of 1944. The de Havilland Mosquito fighter-bomber aircraft of Squadron Leader David "Scotty" Scott (David Buck) is shot down during a low-level bombing raid on a V-1 launching site, and Scott and his navigator/bomb-aimer are reportedly killed. His wingman and friend, then-Flight Lieutenant (later insignia Royal Canadian Air Force squadron leader) Quint Munroe (David McCallum) comforts Scott's wife Beth (Suzanne Neve) and a romance soon develops, rekindling one that they had had years earlier.
After nearly losing his own life on a photographic reconnaissance mission over the Chateau de Charlon in Northern France, Munroe, under orders from a somewhat exuberant Air Commodore Hufford (Charles Gray), leads a Barnes Wallis-type land-use "bouncing bomb" (referred to as "Highball") attack against the chateau. There, following the reported capture by the Gestapo of a French Maquis resistance fighter who supposedly talked under torture, Allied prisoners, including a very-much-alive Scott and men from their group, are held as "human shields." This is seen in a disturbing film dropped by a Luftwaffe Messerschmitt Bf 109 fighter that, in tandem with one other, raided the base, strafing the airfield and killing many personnel.
The Royal Air Force target is an underground tunnel in the grounds of the chateau where new weapons based on the V-1 are being constructed. In a coordinated raid, the prisoners are held in the chapel during Sunday morning mass in order to concentrate them in one place, thus allowing French Maquis resistance fighters to get them out once a Mosquito has used one of the "Highballs" to blow a hole in the outer wall close to the chapel, only not before Father Belaguere (Michael Anthony), a Catholic priest and Maquis agent, is killed by an enraged German army officer, Leutnant Schack (Vladek Sheybal), for refusing to order the RAF men to go back to their cells. The senior RAF officer amongst the captives, Squadron Leader Neale (Bryan Marshall) is killed by German machine-pistol fire during the breakout as comrades make their way with the help of the resistance fighters out of the chateau grounds while the bombing raid continues with a second wave of Mosquito bombers dropping conventional bombs with the intention of completely destroying the building.
Munroe and Scott are briefly reunited after the former's aircraft is brought down by flak, though Scott, still suffering from amnesia and unable to remember even his own name (hence, he sports a chalked "X" on his uniform), rebuffs Munroe's attempt to get him to remember who he is, ignoring mention of even his wife's name. Scott then sacrifices himself while stopping a German tank, saving Munroe and others, but too late to save Munroe's navigator, Flight Sergeant Wiley Bunce (Nicky Henson), but not before Scott says his wife's name.
The next day, after rescue by a submarine, Munroe, along with survivors from the raid, is repatriated and comes back to the base in one of two Avro Anson transport aircraft. There, after being congratulated by his commanding officer, Wing Commander Penrose (Dinsdale Landen), as well as Air Commodore Hufford, he is reunited, albeit separately, with Beth and her brother Flight Lieutenant Douglas Shelton (David Dundas), an ex-pilot who had lost his right hand on operations (he sports a hook in its place) but now serving with the same squadron and in charge of training. However, he deliberately still conceals the secret from her that her now-dead husband had survived the crash that he had witnessed, although, thanks to the German film, both he and Shelton had, in fact, known for some time that he had not been killed as first generally believed.
Although not a sequel, the film is similar to the 1964 film 633 Squadron and is influenced by it, even using footage from the earlier film. The pre-title sequence of the film (including the aforementioned opening music by Frank Cordell) was also taken from an earlier film called Operation Crossbow. Bovingdon Airfield in Hertfordshire was a location for many scenes in the film; four "flightworthy" de Havilland Mosquito aircraft, including RR299, which eventually crashed and was destroyed in July 1996, were based at the airfield. The "chateau" used in the film is actually Minley Manor, the officers' mess of Gibraltar Barracks, near Farnborough in Hampshire, Southern England.
The Highball weapon featured in the film was an actual development of Barnes Wallis's "dam-busting" Upkeep bomb, and the footage seen in the film of Mosquitoes dropping Highballs on land is genuine archive film. Charles Gray's character mentions Barnes Wallis during his briefing, in such a way as to imply that the name was well-known to the RAF men. The special Highball bombsight seen in the film is also a genuine representation of the sight used for dropping Highball.
The film features a memorable music score (starting with 29 pounding bass drum beats to background the V-1 flying-bomb theme of the film) composed and conducted by Frank Cordell. Cordell's score was intended for a soundtrack album by United Artists Records that was never released until Film Score Monthly issued a compact disc recording of his score.
Most reviewers concentrated on the low-budget production values, but the script and cast have also come in for some severe criticism in some quarters.