Diane Medford (Gwili Andre), Tom's shipboard companion offers sympathy, but Lawrence has Lefty tail her, as he already knew the body in the cabin was not his brother.

Tom confronts Arlette with the gun, forcing her to admit that she hid the weapon to protect her love, Harrington who denies murdering Diane and is exonerated by a ballistics expert.

After smoking a cigar, and about to reveal a clue about mass murders to Tom and Lefty, Savitski falls dead, dropping a pile of magazines.

When Tom steps out of the shadows, the pair identify themselves as Mexican counter-espionage agents and explain that Diane was killed because she knew too much.

Tom and Marcia speed off to stop the sabotage, while The Falcon regains consciousness and joins Lefty on a trip to Long Island where German agents have been preparing for an attack, and Harrington is one of them.

After capturing Tom and Marcia and locking them in a bell tower, the agents go ahead with their plan to assassinate a Latin American envoy as his aircraft lands.

RKO had wanted to have Sanders star in one more Falcon film with the enticement that having his brother take over the lead role would further his career.

As it is, "The Falcon's Brother" is just a moderately confusing mystery tale, boasting but three casual murders and the final disposition of Mr. S. Nazi spies, it turns out, are the villains, and that's pretty routine these days.