An American man and an Irish woman fall in love with each other in London while navigating the choppy waters of their increasingly complicated lives. Scorching chemistry, instant pregnancy and genuine disaster provide the foundation for a relationship full of ups and downs.

Sharon faces the reality of having a giant new room-mate in the form of Rob, the man whose child she happens to be carrying, and her brother Fergal doesn't make life any easier. Rob also meets up with an old school friend and comes up with a proper proposal to help Sharon feel better about their situation.

As pregnant Sharon's hormones plague her with waves of different emotions, she has a chance meeting with an old flame, which leads to dinner. Meanwhile, Rob struggles to generate advertising business, since he has very few contacts in London, and begins a clandestine friendship with Chris, who is married to a woman Sharon can't stand.

Sharon's parents visit from Ireland and have a strained introduction to Rob. More health complications create stress for them both, and Rob's secret friendship with Chris explodes in his face.

As the couple plan their wedding, Rob decides to throw a surprise birthday party for Sharon - but also finds himself searching for a new job after his Boston bosses fire him during a video call. To make matters worse, the groom's mother (guest star Carrie Fisher) reveals a big secret he has been keeping from his fiancee.

A heavily pregnant Sharon picks Rob up at the airport after a trip to Boston and tells him she has invited an old friend from Ireland to be her maid of honour. Rob decides to ask his fiancee's brother to be his best man, but Fergal has more important things to worry about - his wife has left him and taken their children. The bride and groom later split up to enjoy their hen and stag nights, both of which spiral out of control.