In April 1943, the peace of small Suffolk town Market Wetherby is shattered when brash American GIs arrive to take over the local base. Shopkeeper Albert Mundy is resentful but his daughter Rosie and her friend Letty are charmed as they take a ride in a jeep. War hero Ronald Dereham is also less than enthusiastic but he observes protocol when he and his wife, local doctor Helen, host a party for Colonel Rufus Krasnowiki and Major James Kiley, before Ronald returns to service. The crack flyer 'Red' Burwash is grounded for an irresponsible show of aeronautics and most of the men are inexperienced so poor weather and a bombing raid from a German plane don't boost their confidence.

The raid isn't terribly successful. Red's plane gets separated from the others and flyer Danny Coogan ends up in hospital. Patricia returns to University and Vi carries on seeing Chuck. Letty is almost caught with Lt Harvey Wallis but – backed by Peter – lies to her father that she was jumped. This fuels local prejudice as Mundy demands action. Kiley tells Helen the matter has been dealt with but will say no more, leading to mistrust.

Vera's younger brother Sid, a spiv, comes to stay, having been bombed out in London. Patricia returns after dropping out of uni and cash-strapped army wife Sally Bilton is offered laundry work at the base by Sgt McGraw. Bad weather and shortage of planes means that the pilots are ill-prepared for their next raid, the Milk Run, in the course of which Wallis is killed just as Letty, having confided in Peter, is about to tell him she is carrying his child.

Jack Blair is grateful to McGraw for breaking up a pub fight started by British soldiers jealous that Rosie is being chatted up by Jones and Stutz. McGraw also comforts Sally, whose husband has been killed in action. Sid's continued presence annoys Mundy, who is not impressed to learn of his brother-in-law's black market deals with Mario. Sid also suggests to Letty, still keeping her pregnancy secret, that she move to London with him.

McGraw and Sally's friendship grows despite disapproval from her selfish mother-in-law Ruby. Mario and Sid organise the Independence Day dance where Vi and Chuck agree to marry, Rosie chooses Jones over Stutz, and British servicemen turn up, not to fight but to unite with their allies. Letty reels in Mario, who charms Vera but is predictably shunned by Mundy.

As mounting casualties take their toll on morale, Red takes a group of flyers to London on leave where Chuck pines for Vi whilst Mario's pursuit of women lands him and Jones in a fight and jail. Stutz takes advantage of Jones's absence to win over Rosie, now working in a parachute factory. Helen is also in London on hospital business and Kiley goes after her, despite her telling him that they should stop their affair.

Hymie and Helmer have a major falling out over Rosie the pub landlords daughter and preparations are getting underway for Chuck and Vi's wedding. Letty is working hard to keep her pregnancy secret from her father and Sally gets a shock when her apparently dead husband turns up.

Vi and Chuck get married but their happiness is short lived when on Chuck's next mission his plane is hit, Chuck is forced to bail out over Germany and Marino is killed.

Pat Dereham tells her father that her mother is having a affair with Major Kiley. Stan Bilton has walked out on Sally but Mac is unsure whether to restart their affair.

Peter Mundy will soon be old enough to join up but his father would sooner be the one to go Elmer bets new boy Billy that he won't make it with Rosie. Major Kiley has agreed with Ronald Dereham that he won't see Helen again.

Vi thinks she may be pregnant, Sgt Billy Colvero may have to be sent home to America after the authorities discover he is only sixteen but Elmer arranges to sneak Rosie into the base for one last meeting. Meanwhile Peter Mundy joins up.

After taking part in a mission Jim Kiley has been shot and his life hangs in the balance. Stan Bilton has been killed killed on active service and his mother blames Mac and Sally. Meanwhile Elmer and Hymie get Peter drunk on a night out.

Kiley tells Helen that after the war is over he wants to marry her; Peter officially joins the army after turning eighteen, Stan Bilton's mother kidnaps Sally's children Betty and William but Mac comes to the rescue. Letty goes into premature labour following an argument with her mother while after a gap of two months Chuck Ericson turns up alive and well.