This installment has the evil Dr. Cracker (Rick Masters) joined by a new doctor, played by Robopimp's Zed Black. Lisa Kinkaid is again on hand as Nurse White. Lisa, who was wasted in Part 3 in a dominant role, is put to much better use this time, as a bound and gagged victim! The tape begins with a recap of the first three parts, which helps bring the story up to speed. Finally, as Part 4 begins, Rick and Zed decide that Lisa would be a perfect "volunteer" to try out their new electro-therapy machine, and despite her protests, she is quickly grabbed and chloroformed and stripped of her clothes. Tied down to a medical table, wires with electrodes are taped to both her nipples, her pussy, even her belly-button ring. Thoroughness counts, I say!

Lisa awakens and tries to object, but her mouth is then filled with a large rubber plug gag, completing the ensemble. She looks incredibly hot all spread out and wired up. Zed cranks up the machine, and Lisa writhes as her body is shocked. Masters directs this scene very well, with lots of shots and angles, and it is a good sequence, although it could have been helped immeasurably by some more emotion and maybe some muffled screaming from Lisa. Being shocked has got to really hurt, but too often, she seems merely uncomfortable rather than in agony. Nonetheless, it's a better-than-average illusion.

Lisa's scenes are intercut with Pamela Price and Chandra Sweet as a pair of sisters who received "the treatment" in Parts 2 and 3, and they are still here in this installment. Brian Dunhill has Pamela tied naked to a chair, panties strapped inside her mouth, while a bound and gagged Chandra watches the procedings. Brian uses a vacuum suction device on her tits and pussy, and while it doesn't really look painful, Pamela gives an excellent performance, loudly moaning and screaming through her gag. She makes a lot more noise than Lisa did in the previous scene, and it at least seems like it hurts. Again Masters shoots the sequence very well, using lots of close, handheld camerawork.

Afterward, Pamela and Chandra are tied together, with Pamela standing with her arms tied above her, and Chandra's face tied over Pamela's bare crotch. Brian, delivering some of his patented one-liners, delivers a nice whipping to Pamela on her chest and ass, taking care of her thoroughly but completing ignoring Chandra. The lovely Ms. Sweet is woefully under-used here. While bound in every scene, she is never the object of any torture scenes, and appears here as mere window-dressing, an odd decision.

Back to the good stuff. Zed now has Lisa tied bent over on the operating table, her ass sticking out. After stuffing her mouth with a cloth and sealing it with duct tape, he raises up the table so that her feet are dangling off the ground, then lubes up her ass with vaseline. What follows is an excellent bondage rape that looks real, and Lisa is much more vocal this time as he thrusts into her. Masters usually pulls off the illusion by using rubber prosthetics, but this time, everything looks genuine. What can I say? It's scenes like this that are the reason I watch ZFX tapes in the first place!

Zed isn't through. He raises the table up even farther, and you can see a bit of cum still dripping from inside Lisa's ass. He then delivers a savage whipping to her bare behind, and the red slash marks are also visible. Masters' attention to detail here is impeccable. Zed whips her to unconsciousness, then sits down. At this point, the tape abruptly ends.