電影《二次人生》講述做事得過且過，活在霧霾天空下的地產經紀志行，一天重遇小學恩師黄Sir ，得悉黄Sir為了兌現亡妻完成10K跑的承諾，即使患病也堅持練習；舊同學兼同事余良委派志行去看管追星一族的侄女-肥妹天心，天心為了一個和偶像一起跑步仔的機會，不惜一切拼命減肥….

志行眼見黄Sir及天心各自為着目標奮鬥，漸漸地被感動，下定決心實踐兒時曾經說過的一句話 「總要為自己人生歡呼一次!!」。

Chi is a lousy real estate agent who doesn't know what to do with his life. One day he meets Mr. Wong, his former elementary school P.E. teacher who is very ill, he insists to fulfil the promise he made to his late wife to participate in the 10K run.

In the meantime, an overweight student Tim Sum is looking forward to join her first 5K run so that she can run with her idol. Being motivated by their passion and commitment, Chi decides to pursue his childhood dream again...