Sergeant Blake of the Northwest Mounted Police is sent to the border to break up a ring of smugglers who are bringing illegal Chinese immigrants into Canada. The ring is led by Ah Ming, a "half-breed" who goes by the name of Dr. Lawler. When Blake encounters Lawler, he is experimenting on a white mouse.
| Actor | Role |
|---|---|
 Lewis StoneSgt. Blake, R.C.M.P. | Sgt. Blake, R.C.M.P. |
 Wallace BeeryDr. Lawler | Dr. Lawler |
 Ethel Grey TerryErimine Reeves | Erimine Reeves |
 Willard LouisSing Lu | Sing Lu |
| BBessie WongChinese Girl | Chinese Girl |
 Margaret McWadeThe Mother | The Mother |
 Pomeroy CannonNot listed | Not listed |
 Anna May WongNot listed | Not listed |