The First to Die at the End by Adam Silvera is the prequel to They Both Die at the End. I did not read the latter.
The book explores the idea of being able to learn your exact death day by buying into a company called Death Cast. The book jumps to various characters (Death Cast owner, an employee and others), but is primarily focused on Valentino and Orion.
Valentino just moved to NYC to start a career in modeling a day before his twin sister. He is at the debut of Death Cast in Times Square when he meets Orion and Orion’s best friend who is like a sister for the first time. Orion has a heart condition and has bought into Death Cast. Valentino decides to join in by buying a one day membership. The very first phone call is made, and shockingly it’s Valentino who receives the call.
This moment speeds up everything, especially Valentino and Orion’s relationship. Orion does his best to give Valentino the best end day possible, all the while not knowing when/how death will come.
It’s a love story first that also raises some thoughtful questions about life and death, fate and the people who come into our lives at different moments.