According to Don Markstein's Toonopedia:
"The Black Terror was pharmacist Bob Benton, who got his super powers the same way Hourman, Asterix, Atomic Mouse and many other old-time superheroes did — by ingesting a substance which we would nowadays call a drug. In his case, it was "formic ethers", which he'd been experimenting with in his spare time. Breathing them gave him super strength, and toughened his skin to the point where bullets would bounce off harmlessly. His main motivation for putting on a costume to fight Japs, Nazis and criminals seems to have been the fact that practically everybody with super powers was doing it those days. "
In the stories the Black Terror's powers are slightly amorphous. Sometimes he's super-strong, sometimes he's almost invulnerable, and sometimes he can run four or five times faster than a normal human.
This story from America's Best Comics #15 from October, 1945 is written by Edmond Hamilton and drawn by Edvard Moritz, while the cover is done by the prolific and amazing Alex Schomburg. I like how the black marketeers have put up a sign "Black Market Headquarters" so that the Black Terror, Doc Strange and The Fighting Yank know they're breaking up the right place!
The first-page caption of "One Corpse Too Many!" explains the whole plot:
"There's mystery a-plenty when young druggist Bob Benton arrives for a secret chemical job and finds his client, Brett Wilkins, strangely vanished! The body of a stranger turns up to confuse the picture until Bob and his friend Tim switch to combat garb as the might Terror Twins and break through the dam of hidden evidence to solve the riddle of 'One Corpse Too Many!'"
This summary reads more like an outline for the writer than something to be shown on the first page of the story. They even mention the conclusion in this brief text box.
A couple story points jump out at me. I love the premise that Bob, as a druggist, is hired to create explosive powder to help the war effort. Speaking of "explosive powder", could they actually mean gunpowder? What scientist could possibly create an anti-aircraft gun, but fail so completely with the gunpowder that he has to travel to another city to hire a druggist to make this explosive powder?
It's also very odd how Bob and Tim decide to travel to Chicago on the train while in costume. Bob says "meet me at the station in uniform, Tim! I think this job is going to start popping from the start!" But, ever more pathetic is Jean's confusion at having the Black Terror travel with her to Chicago instead of Bob Benton. It would be as if Lois Lane was disappointed that she had to share a taxi with Superman rather than Clark Kent. And I love how the Black Terror explains his presence instead of Bob: "he got a more important job and simply turned this over to me!"
The strangest event in the story is where the Terror Twins smash through the dam. You'd think breaching a dam of that size would cause considerable flooding, but the heroes shrug it as easily as they can lift Jean off her feet.
Overall, the story doesn't make a lot of sense. I'm not sure why Dexter wanted his uncle dead, something about an estate but the motivation is weak. I'm also unsure why he thought he needed to create another corpse to prove his uncle's death. The Black Terror and his sidekick Tim spend most of the time in costume, but perform few heroics until the last page, where they nearly flood the town. But, ya gotta love the cover!