In the year 2019, eminent physicist Ye You Ning travels back to his hometown in China from abroad after many years to take care of his ailing grandfather. However, after a thunderstorm, he finds himself transported back to his school days as a student in the year 2006. He discovers that the secret of his time travel lies in the mobile phone of Xia Wen Xi, his optimistic and sunny deskmate. As he attempts to go back to his original timeline by communicating with Xia Wen Xi through the phone and manipulating events in the past, he gets to relive his life in various situations, goes through regrets, and gets to know the gravity of the choices he had made and the true worth of the people he met, including Xia Wen Xi and his old classmates whom he had failed to cherish.