This is one of the best standalone science fiction books I've read this year. I don't want to boil it down to comparisons; nevertheless, I can't help but think that this is like if Blake Crouch were British and wrote a version of Inception. Yet, instead of Leo, you have Dame Maggie Smith stumbling through memories and time. Plus, it adds a "Secret History" style backstory, because every mystery thriller could use a little dark academia. All the elements were the perfect combination, in my opinion. 

I really enjoyed how character-focused it felt. I'm even starting to think that old ladies make the best sci-fi protagonists (read also Remnant Population by Elizabeth Moon). These old fuddy-duddies bring so much heart to a story. 

The way the plot unfolded was satisfying, and the ending worked and made sense in a way. It's one of those books that leaves a major hangover, which is one of the most gratifying feelings a book can produce. I'd highly recommend this read. The layout of the book is engaging, and the audiobook is also great, done with a trio of narrators. Regardless, this is perfect for readers who enjoy science fiction thrillers.