Facing up to their flatlining sex life, Joy and Alan take desperate measures.

Joy and Alan throw themselves into the experiment with surprising results. 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.