An enormous metal rack... for starters.

Karen's eyes remain locked on the toy you'd decided upon as the centerpiece of today's festivities. It gleams, clad in polished chrome and stiff leather, large enough to easily take a person no matter their size. The main body is one big rectangle, set onto a complex mechanism that can raise, lower, and twist the device at will. Thick ropes extend from ports set into each corner and at predetermined points along the border of the rectangle, the corner ones ending in adjustable leather cuffs.

The walls behind the rack are covered in shelves, lined with sex toys and harsher, metal-shod instruments, that Karen's eyes quail and widen when she looks at them, but her gaze returns, inexorably, to the bulk of the machine ahead of her. The rack robs her of her senses, leaves her staring.

'Step up onto the rack, Miss Gillan,' you gesture, a sort of "after you," brush of the hand. The tall woman moves, after a moment of stumbling before the controls on her mind **** her to bend to your command, obediently clambering up the short step up onto the rack. The way it's angled, Karen can comfortably lay back against the metal surface, and though she stays mostly still, you can see her fingers twisting and curling, fidgeting nervously.

There's nothing else for it: she remains in place when you approach her, and allows you to strap first one ankle, and then the other, to the corners of the rack. She flinches when you try to do the same with her wrists, but another command forces her to raise her hands and offer them to the straps, for you to truly restrain her.

But you don't tie her up like this just to have her relax against the straps, surely...

'Alright,' you check the straps, ensuring that they're on tight enough to keep her pinned. 'You may struggle as you wish, now. The fun part's up next...'