Adoara, a marine biologist, Anthony, a famous rapper, and Agu, a soldier who's gotten into trouble for not condoning a superior sexually assaulting a civilian, all met on Lagos' Bar Beach when the aliens arrive on earth. The three of them are weighted down by their own personal problems, but those have to be laid aside as they are pulled under by a tidal wave and spat back out together with an extra-terrestrial being named Ayodele. Lagos is already in a state of great upheaval and the presence of the alien guests, once the fact leaks out, does not help matters. Regardless what happens, nothing will ever be the same again.
In her acknowledgments, Okorafor thanks the 2009 science fiction movie District 9 "for both intriguing and pissing me off so much that I started daydreaming about what aliens would do in Nigeria. This novel was birthed from my anger at District 9, but it quickly became something else entirely." While any overt references to the movie are, as far as I can tell, missing from the finished story, Okorafor provides a telling as well as amusing commentary on how western-centric most science fiction (as well as popular culture at large) is when more than one character bewilderedly asks whether the aliens are lost and if they weren't supposed to end up in New York instead. It is funny, but it also says a lot about how extremely narrow the focus of SF stories and popular culture is when the idea of aliens on Earth is easier to accept than that they would land anywhere but in USA.
Lagoon is a fascinating first contact story, focusing less on the aliens themselves, who remain somewhat obscure both in shape and motives throughout the novel, and more on humanity response to their presence. Many flee from Lagos in fear, but others are more inclined on using the alien presence to their own advantage - to gain money, recognition, fame, power or acceptance. Adoara, Agu and Anthony try to aid Ayodele in her mission to help Lagos heal itself, but it is not so easily done with the country caught up in a state of crisis.
While the focus remains on the three protagonists, several chapters are narrated by other characters which allows for Okorafor to capture how Lagos and its population responds to the presence of the aliens. It is not only the people that is affected, but also the animals, the sea, the roads and even the air itself. Usually I find the use of multiple one-time POV's unnecessary and messy, but Okorafor pulls it off really well, making every character and every voice feel unique and integral to the story, rather than just there to provide a specific clue to the plot. Some of the narrators are somewhat unexpected, which makes it interesting - especially in the first chapter that, thanks to an unconventional narrator in the shape of a swordfish, manages to immediately pull the reader in.
What the story lacks, however, are fully fleshed out protagonists. That Ayodele and her kin remains obscure I can contend with, but, apart from Adoara, the main characters are all a little too flat, and as such becomes rather uninteresting. It is just one flaw in an otherwise great novel, but it becomes a major one when the swordfish narrating one chapter is a more engaging character than the majority of the story's protagonists.
To conclude, the paper-thin characters is a small problem in an otherwise great novel. I am admittedly very partial to any kind of science fiction story that takes place in or focuses on the big blue sea (other noteworthy ocean-themed SF works are Peter Watts' Starfish and Seanan McGuire's short story "Each to Each"), but even putting the beautifully rendered setting aside, Lagoon is an imaginative and well-written first contact novel. I highly recommend it.