Read this one a long time ago and cannot remember the author, title, etc; but remember a fair bit of the plot.
A man is drummed out of a space patrol service for following protocol, firing upon an Earth ship carrying medical supplies after it refuses to submit to random inspection. He begins investigating the Earth men based on his culture's honor code: he must either prove he was right or commit suicide. He eventually finds out that the Earth men are transporting live human cargo for medical supplies, and are cannibals. After they kidnap a woman Captain who traveled with him, he docks with their ship, but creates a deadman switch; if he does not answer a multiplication question in base 8 within a few seconds, his ship will jump to FTL, and if the Earth ship cannot match, it will be torn apart. The Earth men are smart enough to figure this out, but he manages to trap them with the nearly feral live human cargo.