We are told that the Pemalite ship is in danger, even though the Chee moved it to a safe location and area and are not on-screan requesting the Animorphs to interfere. Seriously, couldn't they have asked Erek what was up?
But, no. Jake has heard of Visser Three's new submarine and wants to sink it, which is enough cause in and of itself, but we're also subjected to a description of a tortured Hork-Bajir. The Visser is not very good at science. Also, aren't the Hork-Bajir supposed to be a rare resource? There are not enough of these bodies around to fill vacancies in the Yeerk army, but Visser Three can just throw 40 of them away on a bogus biological experiment?
In the course of chasing down the submarine, the Animorphs discover an underwater civilization that is as backwards as it is implausible. I'm not going to talk any more about it. Moving on.
Next: 'The Weakness'