This is a good story with a solid plot. Adding dates to the events helped me to know where I was in the story, especially for the long jump forward in time for the last part. The exposition at the beginning explaining why whaling was such a big deal was a good bit of historical background.

One thing that was not necessarily needed for the story was Mitchell being seasick. It was visual, but there seemed to be no connection between this plot point and the overall story. Just something to think about.

The lights in the distance and Harold's nonchalant explanation were a good foreshadowing of events to come.

The slimy monster could use a little more description. It's very hard to know what it is. When it attacked Harold and held still for a moment would have been a good time to describe it. I am also not sure if it entered Harold's body or if it only clung to his chest from the outside.

Lastly, the moment when Mitchell thinks of his son for the last time, it's as if there is some detail missing. Why? What happens at that moment? More light? A big sound?

The ending is great. Although I wonder why Clara is worried about the military breathing down her neck. That's a pretty specific worry for a fourteen year old and it's not explained from context.

Hopefully this review is useful to you.