If Melody hadn't run out of de-icer that day, she would never have slipped and banged her head. She wouldn't be left with a condition that makes her sing when she's nervous. And she definitely wouldn't have belted out the Arctic Monkeys' 'I Bet You Look Good on the Dancefloor' in assembly at her son's school.
If Dev hadn't taken the kids to the zoo that day, then the accident wouldn't have happened. He wouldn't have left Flynn and Rose without a dad. Or shattered the love of his life's heart.
But if they hadn't seen the missing person report that day, they might never have taken the trip to Cornwall. And, in the last place they expected, discovered what it really means to be 'Us'.