We open with some of the usual bickering between the Human Torch and the Thing, which gets interrupted by Doctor Doom - a name Mr. Fantastic knows and dreads. Demanding the Invisible Girl as a hostage, Doom demands that the rest of the FF go back in time and bring him the treasure chest of the famed pirate Blackbeard. In an amusing twist, thanks to the Thing's disguise, he actually starts the legend of Blackbeard, which leads to some solid character moments when he's tempted to stay in the past, where he'll be respected and admired instead of feared as a monster, although he eventually comes to his senses. However, upon their return to the present, they try and double-cross Doom, who leaves them to perish in a death trap before the not-so-helpless Invisible Girl saves the day. Doom escapes, a future reckoning all but certain.
Without those, there's not much about Doctor Doom that really stands out. The combined talents for science and sorcery are interesting, but that's about it. He's just a stock bad guy in armor who wants to rule the world. It's serviceable, especially for when it was written, but much of what made Doom such a compelling character and dreaded figure was yet to come.
I might not think much of "Prisoners of Doctor Doom," but I'll readily admit there's still some good stuff in here, and it still deserves credit for unleashing one of the best Marvel villains on the world. Just because it's not my thing doesn't mean it won't be yours, and finding this story won't be too hard. It's been reprinted many times, most recently in a True Believers edition that shouldn't be too hard to get a hold of. Check it out for yourselves and make your own call.