The ghost was on a mission that was just coming to an end. They split up and searched the rainforest in an area of southern Mexico, looking for an item where drugs might have been.

When the Ghost comes out to a small bay, he meets the Siren...

The Siren had a human body, but her hair was blue, her skin was pale with a slight glimpse of scales, and she had a long, sinuous tail instead of legs

You did not notice the presence of the Ghost, as you were sitting on the shore, with your back to him