Soul Eater, Vol. 12

The DWMA student body is still reeling after the news that one of their
own is a witch. But as one young witch flees Death City, another has
come back to DWMA hoping to strike a deal with Shinigami-sama. Medusa
has already proven herself a traitor to the school, but the information
she offers is critical to DWMA's efforts to take down Arachnophobia and
curb the spread of madness. Can Medusa be trusted to lead a team of
students into the heart of enemy territory?!