A couple of American soldiers of fortune are hired by the wife of a Chinese general to deliver a priceless diamond to a shopkeeper in Shanghai in this low-budget whodunit from the RKO "B"-unit. Just as the gem reaches its destination all hell breaks lose. When the dust settles, the diamond is gone and Tom Baldwin (Vinton Haworth) and sidekick Joe Dugan (Gordon Jones) are left with a group of highly suspicious witnesses. The entire assembly, including pretty but mysterious Jane Dunn (Constance Worth), then boards a liner headed for San Francisco. After several shipboard murders and the revelation that Jane is a custom agent, the culprit is caught red-handed. A lady detective ought to have made a refreshing change but, sadly, China Passage delivers few surprises and the armchair detective is never truly tested. Usually a supporting player of little merit, Vinton Haworthproves a rather weak-chinned hero and is certainly no match for the ash-blonde Worth, an Australian actress turned Queen of Hollywood B-movies. The rest of the supporting cast perform their assignment in the expected manner, Dick Elliott being the standout as an eternally tipsy traveler. China Passage was directed by Edward Killy, who later helmed the studio's series of Tim Holt B-Westerns.