Based on a (very) short story by renowned science-fiction legend Robert A. Heinlein, this shit literally exploded my brain and imploded my heart. Just a really, really well done movie from top to bottom with extremely good acting.
In essence it's a movie about a specific paradox of time travel, and it's done better than any other time-traveling movie (or story) that I've come across.
You'll read some poor reviews because a large, 30min section is largely just monologue over different flashback scenes, but it's interesting and helps the characterization, so in my opinion makes the movie. In fact, without the parts that most reviews deem "boring" this movie would have been utter shit.
Also, the lead, Sarah Snook, is one of the most beautiful women I ever did saw.