Jack and Kay's move into a new neighbourhood is welcomed by their friendly neighbours, Doug and Andrea, who invite them to their weekly summer garden party – but they are unaware the party is for swingers to meet and have sex with strangers. Meanwhile, Jack's work life takes an interesting turn when he is recommended for promotion into the position previously held by his best friend, Kevin, who is being squeezed out of the company. Jack, however, is unaware that Kevin and Kay are having an affair.
Jack and Doug's friendship begins to grow, while his marriage continues to fall apart. Matters aren't helped when he and his daughter, Maggie, spot Kay and Kevin sharing an illicit kiss in a hotel car park. Jack decides to take a leap in the dark and join in with the latest swingers party, pairing Kay off with a fellow party-goer. Kevin's leaving party at the firm is interrupted by an angry Maggie, who confronts him over his affair with her mother. Don turns up on Jack's doorstep after being thrown out by his wife.
Jack suspects that Doug may be involved in the disappearance of their neighbour Lillian Stokes, after he discovers Doug has disposed of a number of letters addressed to Lillian that he claimed he was going to forward on to her new address in New Zealand. Jack and Andrea choose to forgo a night of passion and instead go on a 'first date', while Don's continued deteriorating health leads Jack to a difficult situation. Later, he arrives home to find Don being taken away by paramedics, having had a heart attack.
Jack and Kay attend a swingers' party at a country hotel, but the night quickly descends into disaster when Jack finds an inconsolable Doug, who claims that he has accidentally killed his latest sexual partner when a game of foreplay went too far. Doug persuades Jack to help him dispose of the body, but after a close shave with the police, Jack is led to believe Doug may have lied to him all along when the woman he is supposed to have killed turns up in the hotel bar where Jack is holding a business meeting.
After the police confirm that the body found is that of the woman Jack knew as Janet Taylor, Jack realises that Doug intended to frame him for murder all along. Andrea tries to help confirm Jack's suspicions by leaving the house unlocked when she and Doug go on a night out, but it doesn't take Doug long to work out what is going on, and he has Jack arrested for burglary. Meanwhile, Kay continues to delibrate whether or not to keep the baby, but her decision isn't helped when Lauren tells Sam that the baby is his.
Andrea seeks solace in Jack's seaside hideaway, but it's not long before Doug catches up with her. Kevin gives Jack a secret tip-off about the supposed deal he is about to close. Doug goes on the rampage and digs up Jack's living room floor with a power drill, only to reveal the location of the missing body of Lillian Stokes. Just as Jack realises what is going on, he arrives home to find Doug has taken Maggie hostage with a knife to her throat – forcing Andrea to make a shock decision that will affect everyone.