The plot of this film picks up where ''The Mad Doctor of Blood Island'' leaves off. Upon leaving Blood Island, the ship carrying Dr. Bill Foster (John Ashley), Sheila Willard, her father and Carlos Lopez explodes and sinks after mutated "chlorophyll creature" Don Ramon Lopez (the titular "Beast") is found secreted on board and goes on a rampage, destroying the ship. The monstrous Don Ramon washes up back on Blood Island and heads into the jungle. Dr. Foster is the only other survivor, and after a few months recovering in a hospital, he heads back to Blood Island on another ship. On board is reporter Myra Russell (Celeste Yarnall), who is investigating the explosion of the ship.