Rosie is incredibly excited. Grandad - aka Gandalf - is finally coming because there's going to be a birthday with lots of presents - albeit Ben's birthday presents.

A birthday meal out at a restaurant descends into chaos, but luckily Grandma has bought Rosie some presents to distract her. Everyone in the restaurant assumes it's Rosie's birthday, which in turn leads to yet more carnage. The only person unaffected by all this is Ben - she's just Rosie, after all.

In the earlier timeline, Simon and Emily are effectively leading separate lives, until Rosie's first laugh finally helps them move a little closer.

Simon's mum and stepdad have come to stay. They want to take Ben back down to Devon for three weeks in the summer, which causes Simon and Emily to wonder why they are not willing to take Rosie. While Simon and Emily go on a rare night out, nana and grandad look after the kids, but when they return, they sense that something has gone wrong.

A trip to Rosie's favourite place - the swimming pool - ends in disaster when she decides she hates it. Emily begins to wonder if it's just that Rosie wanted to do something else. Simon goes off to take pictures of all the places they regularly visit to put together a booklet. Rosie types 'onetwoman', which Emily and Ben try to cross-reference with her iPad to figure out what it means. In the earlier timeline, Emily's academic nature and desire for answers is yielding much less success. At their first appointment with a genetics doctor, she finds him a like-minded soul who seems to view Rosie as a problem to be solved.

It's bath night for Rosie which, as usual, ends in bubble-filled carnage as both Simon and Emily battle to get an unwilling and slippery girl out.

Emily strategizes that she can trick Rosie into getting out by putting the bubble bath tantalisingly out of reach and secretly waiting outside to pounce. This game of 'bubble chess' swings back and forth as Rosie works out how to stay one step ahead of her mum.

In the earlier timeline, Emily struggles to connect with Rosie, whereas Simon has a bonding moment when she does the biggest poo he's ever seen. Tensions build between them over whether, given a magic wand, they would change Rosie.

Rosie is a nine year-old girl with a severe learning disability, the result of an undiagnosed chromosomal disorder. She lives with her dad Simon, mum Emily and brother Ben.

It's a typical Saturday for the family, one which revolves around trying to get Rosie to do simple things - go to the park for some fresh air, eat her lunch, go to bed. Rosie leaves a trail of destruction in her wake, ramping up Simon's stress - in his short-sighted attempts to get her to go to sleep too early, he only makes things worse.

An earlier timeline shows how Simon and Emily first confront the inescapable truth that something is wrong with their baby daughter.