The story starts with explaining how the Americans are worried about events in earlier books, starting a dangerous experiment and sending exchange students over to find out whether or not it was magic and if so which magician cast the spell. Angelina Kudou Shields is send over to Japan as an exchange student, she is also Sirius, the leader of the American magical elite military unit. Things get even more complicated when "vampires" arrive on the scene, killing innocent civilians and triggering a massive hunt in which Tatsuya is drawn because Leo was attacked by one.
As usual the story is brilliant in its world building. Small titbits are revealed at logical places of the story, showing a grim and dark world under a veneer of civility. New characters are carefully introduced or deepened and we get to see the story more from other peoples' perspectives then in previous parts. It also includes some good action scenes and as always I enjoy the magic system. I like how the people are complex, the absence of Japanese light novel/anime trope characters and how the main character has actual male friends. The sister/brother relation might be a bit disturbing, but it fits the world since it seems to be mostly the result of genetic and magical manipulation of both as young children to both increase their magic and to keep them under control.
The ending is a bit abrupt, even though not a cliff-hanger, so I would advice to read all three parts of the arc at the same time. The story can at times also be a bit slowed down by the world building details. I find it a bit odd on the reasoning on why a military force would send soldiers for what is basically the work of a spy. It makes a good story, and fits the idea of ridiculously competent high schoolers (which the author admits is a bit far fetched). It wouldn't have a high chance of success. The conflict between the two factions of Japanese authorities seem a bit odd as well. It seems a bit extreme. There is also relatively little Tatsuya, he is but a bystander at first by design. Still it gives the opportunity to see some of the characters involved in the story.
Still, a great continuation of the story.