When will the world end? With a massive comet, hurtling toward Earth, humanity now knows the exact date. 17-year-old Simon wants to spend his last weeks with the people he cares about most, especially his ex-girlfriend, Tilda. Since Lucinda was diagnosed with cancer, she's retreated into herself. Reaching out to her former best friend Tilda seems like a good first step. Then Tilda is found dead and accusations start circling that Simon is the killer. As the days tick down, Simon and Lucinda search for the truth, but the more they uncover about Tilda's final days, the clearer the things that really matter become.