“Intermediates: A Cuckoo For Mankind” by D.W. Cook

They co-evolved with us. They are unknown to mankind, and have our external physical appearance, with one difference: They phase from one gender to the other, as part of their reproductive cycle, seducing unwitting humans of both genders. Their continued survival as a species depends on taking their offspring from duped human mothers and in regarding mankind as a useful tool. They call themselves “Intermediates”.   https://www.amazon.com/dp/B06XB7RKSS/

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