Tractor repairman Steelhead (Jackie Chan) sneaks into Japan illegally to look for his girlfriend Xiu Xiu (Xu Jinglei). He joins old friend Jie (Daniel Wu) and a band of Chinese illegal immigrants living in the shadowy fringes of Japanese society. Forced by circumstances, Steelhead rises to become the new leader of Shinjuku with the help of yakuza boss, Eguchi (Masaya Kato).

After Steelhead gets legal status to live in Japan, he retreats to settle into a quiet life with his new girlfriend Lily (Fan Bingbing). But their peace is interrupted when policeman Kitano (Naoko Takenaka) tells him that his brothers are now committing serious crimes. Steelhead goes with Kitano to persuade his comrades to turn over a new leaf. His good intentions are misunderstood and he finds himself surrounded by former allies. Meanwhile, Eguchi is intent on using this chance to get rid of Steelhead and Kitano once and for all. A bloodbath is about to begin...