They Both Die at the End plays on the idea that you should live every day as if it's your last. What would you do if you knew you were going to die today?

We might like to pretend that if we had one last day, we'd do something amazing, but Adam Silvera is fairly realistic about what is possible, especially for two teenagers. They say their goodbyes where they can and go to experiences designed for Deckers. A differentiation is made between Deckers who have been ill for some time and those like Rufus and Mateo who had no idea their end was imminent.

Mateo and Rufus would probably never have been friends without Last Friend. Rufus is a foster kid and from what we know of Mateo, he doesn't have to worry about money or safety. But they have both lost family. It's about friendship and preparing for death, sharing in the grief. It's a message to live each day as much as you can, because you never know when that day will be your last.

It's intentionally vague about how Death Cast works. You have to just go with the flow and imagine it as a Final Destination scenario; when it's time, it's time and you can't cheat fate. A little of the wider implications are explored, but I kept having questions about it all. Is it really better to know you're going to die? You get to say your goodbyes, but also your final moments must be tainted by that knowledge. Has reckless behaviour increased because people feel they are immortal if they don't get the call? What about mass-casualty events... Do they not want to try and stop something if there are indications that hundreds of people are going to die in one place?

It was a bit too convenient that both teenagers already had had a lot of experience with untimely deaths. Poor Lydia, losing both her boyfriend and best friend so young.

Even knowing the ending didn't make it any less heart-breaking.