Of course it's the Doctor

The distinct sound of expensive dress shoes stepping down the cold stone steps rang throughout the cavern. Kim slept as the doctor lowered his wife's expired body to a cart and wheeled her from sight. When he was finished, he returned to wake the sleeping Kimberly.

"Good morning my dear." He said running his hand though the dark hair of the sleeping, naked Kim. Her eyes fluttered open to see his face along with the empty wall. "We can't have you and your husband mucking up my experiments and research. So you must be dealt with." He said releasing more gas into her mask. "It will take a few birthings and then you will no longer need this aphrodisiac gas, your body will have adjusted to its new role."

He unchained the helpless Kim from the stone table and lifted her limp body into his arms. She shivered from the cool air of the cavern and her body still drenched in sweat from the previous night. He carried her to the wall and sat her down on her feet. Quickly her wrists were chained spread above her followed shortly by chains spreading her ankles wide.

Kim's could feel everything, the cool cave wall against her naked back and ass, the metal chains circling her wrists and ankles, and the doctor's warm hand caressing her curves and chest. The gas filling her lungs kept her docile and aroused. She could feel her own unwanted arousal trickling down the inside of her thighs. She managed to look down at her helpless body to see her own moisture slide past the dried cum that covered her legs and pussy mound. She took a long look at her ample, perky breasts as her mind filled with an image of the woman chained to this same wall.

The doctor left Kim to prepare the next specimen. For a moment he considered returning and sampling the pleasures of Kim's body he had offered to his friends the night before. He returned his thoughts to what creature to test on Kim's fresh body.