I tend to not be able to access BL until quite late at night, when I get out of work and head to the gym, and I don't write posts until rather later, when I can actually type on a keyboard rather than peck away on my tablet. Because of that, it looks like I'll have the opportunity to read and enjoy everyone else's choices for the BookADay before I post mine. So I'm going to modify it a bit and try to post a book that hasn't yet made it onto my feed.
Given that the theme is UFOs, I decided to plump for scifi rather than fantasy.
For me, the Vorkosigan Saga was the natural choice.
Most of the Vorkosigan Saga follows the escapades of Miles Vorkosigan, a terrifyingly precocious and ballistically driven young man from the planet of Barrayar. Due to a teratogenic mutation in the womb, Miles is well under five feet, and his limbs are as frail as his will is adamantine,. From Miles' perspective, his physical handicaps only mean that Miles has more to prove. His story is not so much a saga as a series of absurd situations and narrowly averted catastrophes.
Bujold tells a lighthearted, entertaining story, and she never takes herself too seriously. Yet she also manages to wedge in quite a bit of political commentary and interesting scifi twists.
If you're a fan of scifi, it's definitely a series to try. I'd suggest starting with Warrior's Apprentice, which is the start of Mile's story.
Actually, I reviewed it a while back--my review is here.