John Ashley returns, this time as a different character, Dr. Bill Foster, who goes to the infamous island to investigate reports of people with green blood. Angelique Pettyjohn is Sheila, who goes to the island to track down her long vanished father, who is a drunk.
Dr. Foster discovers that Dr. Lorca is doing experiments with chlorophyll obtained from a strange plant (which looks like the weird trees from BRIDES OF BLOOD) and has turned one islander, Don Ramon, into a flesh rending creature. Alfonso Carmajal (who is also in all three "Blood" movies,) is sinister looking henchman Ramu.
I didn't like this quite as much as the first movie, perhaps because it's more heavy-handed with the whole mad scientist angle. And I liked the radiation/mutant scenario established in the first movie, which is all but ignored here.
The best part of this is the prologue about taking "The Oath of Green Blood", which is just, well, creepy.