This intelligent drama follows a group of medical scientists as they attempt to find the cause behind the dreaded yellow fever. It is just after the Spanish-American War, and Stone (playing Major Walter Reed) is head of a medical staff stationed in Cuba. Convinced he has found the carrier of yellow fever (nicknamed “yellow jack” by the men), Stone needs five volunteers from the US Army to serve as human guinea pigs. Montgomery heads up the enlisted volunteers, understanding well the unknown dangers of what he is about to undergo. Montgomery is bitten by some mosquitos carrying the yellow fever; three others stay in a “dirty room;” the fifth must sleep in the bed of a dead yellow fever victim. The film wisely concentrates on the ordeals of the five volunteers. This is a story filled with tension and suspense, backed by an underlying humanity. Montgomery (taking the role created on Broadway by James Stewart) is excellent as the lead volunteer, projecting a stoic image as he submits to the unknown. The film is slightly marred by an unneeded romance between Montgomery and camp nurse Bruce. Their scenes together, though well played, seem out of place and detract from the already strong drama. The ensemble is a good one, with Stone, Devine, and Ebsen particular standouts.