#005, in which Danny-boy knows why the caged bird sings

MYSTERY MEN #5, December 1939. In the Beetle's 5th published adventure,and first 5-pager, a few interesting things develop. First we get a name to the pharmacist/scientist who helps Garret behind the scenes; Dr Franz.
Here Franz uses make-up techniques to alter the Beetle's face to look considerably older.
One can assume that the beetle gadget in this story, a hidden compartment in his belt, was also designed by Franz.

The chainmail of BB's costume is also mentioned specifically for the first time, although it's particular qualities and materials have yet be revealed. And the ongoing struggle of Mannigan to capture the vigilante Beetle gets closer as Mike cosh's Dan on the head, (although to little effect).
The Beetle's costume is virtually unchanged this time around,save for a small beetle emblem on the forehead of the cowl.The buckle also alternates from yellow in most panels to red in the close-up panel of the secret compartment.

This story is reprinted this very same month in the first issue of THE BLUE BEETLE, curiously though, with only 4 pages.