After detective Natsumi Yukihira brings an end to the police hospital terrorist case, Natsumi is transferred to the Nishimonbetsu Police Station in Hokkaido. Meanwhile, a series of grotesque murders occurs in downtown Tokyo involving nails placed in the body of the victims. The fingerprint of Natsumi's ex-husband, freelancer journalist Kazuo Sato, is found on the the body of a victim and Kazuo is placed on the most wanted list. Soon after, Kazuo finds Natsumi and hands her a USB memory stick. The device contains information on a secret organization within the police department. Kazuo tells Natsumi that the series of murders are warnings and suspects become the next victims. Natsumi is then arrested as a suspect. Tokyo prosecutor Katsuaki Murakami appears at the Nishimonbetsu Police Station to investigate.
豊洲警察病院占拠テロ事件解決後、東京を追われ、のどかで平和な北の大地・西紋別に勤務していた雪平夏見に連続殺人の容疑がかかる！
警察の内部情報が隠されているといわれるＵＳＢを巡り、元夫、同僚、上司、検察、凶悪犯罪者ら、雪平に迫る男たち。冬の北海道から始まり、様々な思惑が絡み合う緊迫の逃避行。雪平夏見は誰を信じ、誰に裏切られ、そして、誰を裏切るのか。
警視廳檢舉率第一位的冷面女警雪平夏見（篠原涼子 飾）如今在北海道西紋警署刑事科供職，並與上司一條道孝（佐籐浩市 飾）展開新的戀情。與此同時，東京方面接連發生三起射釘槍殺人事件，最終的矛頭全部指向了雪平的前夫佐籐和夫（香川照之 飾）。豈料佐籐就在與雪平見面不久後也慘遭殺害，雪平則意外成為嫌疑犯。為探求真相，雪平假意劫持來自東京的檢察官村上克明（山田孝之 飾），並最終聯合一條以及三上薰（加籐雅也 飾）聯合展開調查。而關於藏有巨大機密的USB，其謎團也久久未曾揭開……
