There are so many things wrong with that cover, starting with the fact that I really don't need to see the Sub-Mariner's butt so prominently featured. Note that Sue, who's a little closer to us than Subby, looks about three feet tall.
As the story begins, the FF is returning from their trip to the moon, as shown in FF #13. They're mobbed by the public and the media, giving Stan and Jack their usual opportunity to show us their powers on the fly:
After they get back to the Baxter Building, Reed catches Sue mooning over the Sub-Mariner.
And it turns out that she's not the only one thinking about Prince Namor. The Puppet Master, who apparently died at the end of FF #8 is still alive and is planning to use Subby as his weapon against the FF. Namor summons Sue to meet him via a "Mentofish" which can communicate via telepathy with any person on Earth.
Here's a little clue, Sue. If you're sneaking around on your fiance to see somebody, odds are you really do care for that somebody.
When she meets him at the docks, he gains control of her with a hypnofish, and sends her to his undersea lair. Of course, it's really the Puppet Master pulling the strings:
A classic "evil genius" moment if ever there was one.
An apparition of the Sub-Mariner appears in FF HQ to inform them of Sue's capture. Reed, Ben and Johnny head off in search of Prince Namor, with the convenient-for-plot-purposes addition of Alicia. Subby captures them with the aid of yet another improbable form of sea life:
Mentofish, hypnofish, and chloroclams; Namor's got them all! And another to help him handle the Torch:
Meanwhile, Sue is being menaced by a giant octopus, which gives Reed the clue that Namor is being controlled by another. Ben attacks the beast and hurls it off into the depths, where it encounters... you guessed it:
But he discovers that the octopus is mindless, and thus immune to his control. It apparently kills him, releasing Namor from his mental control.
Comments: A sub-par issue. I never cared much for the Puppet Master, and the Sub-Mariner's convenient sea creatures get less and less believable as the story goes on.