Therapist Joy Richards tries to maintain the spark with her husband Alan, following a cycling accident that has put their sex life on hold. Suddenly Joy and Alan find themselves drawn to new people, and both are tempted to make the ultimate indiscretion. With their marriage in crisis, Joy comes up with an audacious, unorthodox but potentially brilliant proposal that will have huge ramifications for the future.
Joy and Alan put their daring plan into action with surprising results, but how will other people react when they are told the truth? Tom shocks best friend Michelle with a peculiar proposal. A disastrous date for oldest daughter Laura ends with a shocking revelation.
Joy must deal with the fallout of Laura's discovery. The rules of the experiment are put under serious strain as Joy bumps into first love Lawrence and Alan's connection to Claire becomes more intense. Meanwhile, mysterious memories from her past continue to plague Joy, jeopardising a relationship with a client. Tom's practice with Michelle awakens surprising new feelings between them.
Joy and Alan's experiment, and the marriage itself, faces its biggest test yet as public and private factors threaten to tear the two of them apart. Tom must finally figure out who he wants and exactly how he's meant to get them. Events place Alan's job in jeopardy, while a bereavement in Lawrence's life brings him and Joy ever closer.
In the midst of all the turbulence in her life, Joy's regular therapy session with Angela becomes an in-depth exploration of the secrets Joy has been hiding from everyone, even herself.
Joy and Alan face up to the seismic changes in their lives and try to decide if the choices they have made are the right ones. After a tense encounter with Claire, a lost and lonely Joy takes a risk on love and goes on a bold journey. Tom's new relationship progresses in a surprising way, and Laura figures out exactly what, and who, she wants for herself. And Joy makes one final decision about the future.