Death Note another note is a side story Light Novel retelling the events of the Los Angeles BB murders. This story is completely detached from the show aside from sharing characters and certain worldbuilding ideas. The main thing here is that if you love L, than you'll love this story. If you love classic murder mysteries, then you'll love this story. Though for this one, a requirement is watching or reading the original Death Note at least before you start this.

This story follows the story of Naomi Misora, an FBI agent currently on leave for making a grave mistake. Her punishment is to be completely removed from her job, and this is where L contacts her about a series of murders taking place in Los Angeles. He needs her help, and that is the gist of this story. I don't want to spoil it because despite the short length of this novel, it is a very well written and thoughtfully put together detective mystery story. If you love L as a character and wanted to see more of him being a funny and badass detective, then this story is for you.

Now onto my very brief thoughts.
I'd rather you read the story than a long ass review from me. This story is coming from the author of the Monogatari series, and it shows. The dialogue is one of the best things about this Light Novel. The back and forth between Naomi Misora and Ryuzaki are witty, funny, and most importantly, interesting. For a story like this to work, you need both the writing for the mystery to be air tight, and interesting. Mystery stories are not interesting if there are lots of plot holes, and they also aren't interesting if they're boring. There is a balance that needs to be struck to make a story like this work. Thankfully Nisioisn makes it work in spades. This story is probably one of the most interesting things I've ever read from Death Note. I was lost in the well crafted mystery, and it made me love Naomi Misora, a relatively worthless character in the original series.
I'd say that the dialogue in this was better than the anime or the original manga. There is just something to be gained from Death Note being in this style. I'd love to see more Death Note side mysteries written in this light novel format, but I'm getting off point. Essentially this story adds more contextualization to Naomi Misora and L's relationship, and really makes what happens in ep 8 of Death Note that much harder to rewatch. I love Ryuzaki even more after reading this light novel and I think that this is a really solid read. If you love Death Note, I really think you'll love this light novel as well. Very simple, but executed perfectly.