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My kids read a YA science fiction novel about three teens who survived a world-wide catastrophe by hiding in an underwater cave that they reached with a mini-sub. At the urging of my kids, I read the book and, now that I'm trying to recall it, they have no idea what I'm talking about.
The details aren't all that clear in my mind, but there was some sort of catastrophe, possibly begun by radio communication with aliens, that ended up killing everyone else except two boys and a girl. Time travel may have been involved towards the end of the book. I would have read this sometime in the last five years.
It may have taken place in Australia or New Zealand.
I'm hunting for the physical copy of the book, but we have so many books and it could have been given to a friend of theirs, so I'm not too hopeful. I'm trying to put a list together of all the books I've ever read, and this is just one more I want to capture. I know that's a hopeless and vainglorious goal, but still.