本剧改编自David Nicholls的同名畅销小说《一天》。
　　1988年7月15日，Emma Morley（安比卡·茂德 Ambika Mod 饰）和Dexter Mayhew（利奥·伍德尔 Leo Woodall 饰）迎来了自己的毕业之夜。尽管大学即将结束，不过这是两人第一次跟彼此说话，第二天早上他们便各奔东西了。第二年、第三年，以及接下来的每一年，在这平凡的一天，他们会是什么样子呢？每年的这一天，Dex和Em都大了一岁，他们见证了彼此的成长变化，经历了分分合合，体会了喜怒哀乐。

　　In the exciting fourth season, we fast-forward six years, discovering that Nikki (Esther Smith) and Jason (Rafe Spall) are experienced adopters having built a lovely little nuclear family, enriched by an extraordinary support network. However, as their teenage daughter, Princess (Scarlett Rayner), starts to yearn for a connection with her birth mother, Nikki and Jason find themselves confronted with the ultimate test of their parenting skills.