The 2nd installment to the Darker than Black series. This follows Suo after her house has caught fire and she crosses paths with the previous protagonist Hei. He is searching for a lost friend and takes pity upon Suo and allows her to tag along with him. Together they start to unveil Suo's past and her relationship with her family. As they dig deeper, they discover that somehow what Hei was searching for ties in with Suo. They soon learn a dark secret that changes everything.