The Microscopic Army!
Jack Kirby (writer and artist), Rosalind Kirby (inks)
1st of 4 stories published in Yellow Claw #3, 02/1957.
A band of paid assassins working for the Yellow Claw walk through a "great wire cage which glows with a strange light" and comes out the other side greatly reduced in size to about 1" tall. They are then able to get into place normal sized people could not. After capturing the device, Jimmy Woo gets shrunk himself to stop them.