Turbulent lovers Rob and Sharon arrange an ill-considered party to enable friends and family to meet their newborn baby. Unfortunately for Sharon, the gathering coincides with a disturbing revelation about her father's health, a visit from Rob's mum, and an unfortunate incident with the family dog.
A sexually frustrated Rob is disappointed when Sharon's psychologist prescribes antidepressants, and not more sex, as a treatment for post-natal depression. However, an outlet for his pent-up libido arrives at work in the form of an attractive new French colleague Olivia, who he quickly engages in what starts out as harmless flirtation. Meanwhile, now that she has been suitably numbed, Sharon finds herself capable of contemplating the world of mother-and-baby classes, but when her only 'mum friend' Sam goes AWOL ahead of a session, she is forced to deal with the dreaded 'mombies' alone.
Sharon decides that she and Rob should inject some passion into their love life. When her advances don't go to plan, Rob suggests a weekend break in Paris. While Fergal looks after the kids, Sharon develops an appetite for a holiday drink.
As Rob and Sharon celebrate a tainted wedding anniversary, Fran and Chris are drifting further apart. Elsewhere, Dave's flourishing love affair with Catherine - a high achiever he's met through AA - is gathering momentum.
Sharon decides to return to teaching but her meeting with the head mistress becomes more of an outpouring of her grief. Meanwhile, Rob feels awkward around Olivia due to her indecent proposal and Dave's life spins out of control following his split with Catherine, and Sharon's brother Fergal fails to repay the money Rob secretly lent him.
Rob has told Sharon about the Olivia situation, but the news is badly received, and she throws him out of the house. Unfortunately for him, the first person he can turn to is Dave, who is in the middle of an epic post break-up bender. Sharon tries to reach out to Rob, but after a brief reconciliation it turns into a major argument which sends the pair into a spiral of bad behaviour. For Sharon it's a night out with 'party pal' Kate, and for Rob it's the surprise decision to have a drink.