The titular Horse-Man was a centaur who led a peaceful existence among the virgin forests of remote pacific island Isla Verde.
But the Horse-Man's idyllic paradise is disrupted by the arrival of a film crew on a location shoot. Fascinated by these strange two-legged creatures who are similar to him and yet aren't, the centaur observes the humans from a distance. But it isn't long before he gives himself away.
The Horse-Man rescues Chris from the river and tries to nurse him back to health. Later, Chris asks the centaur to take him back to their camp. Unfortunately, Chris dies from his injuries on their way there.
When the Horse-Man is sighted running off with Chris' body, Rez is quick to accuse him of killing the actor. Gilda, however, has her doubts, noting that the centaur's careful manner in carrying Chris were not the actions of a killer.
Some time later, Gilda returns to the island to retrieve Chris' body and seek out the Horse-Man. To find out the truth behind Chris' death, Gilda teaches the Horse-Man human speech (he initially could only communicate by making horse-sounds) and gives him the name Sentauro.
As Sentauro spends more time with Gilda, he finds himself becoming attracted to the beautiful actress. But Gilda explains to him that she only loves him as a friend and her heart still belongs to the deceased Chris.
Through Sentauro, Gilda determines that it was indeed Rez who killed Chris. But this revelation opens up another dilemma: how do you convict a murderer when the only eyewitness to the crime isn't human?