Mark would have to do this very carefully. He couldn't afford his boyfriend seeing him like this as there'd be no way to get him to drink the potion, so he'd have to set some sort of trap. He started writing an invitation note, which was harder than usual because he lacked any feelings for him now, but he managed:"Dear Jake, I haven't seen you in such a long time. Why don't you come over over sometime? Really miss you. xxx Mary" He sent the note, changed clothes and waited for the day...
Jake came in - he had a house key - and looked around, saying "Mary?" a few times to see if she was home. He found a note on the table that said:"Dear Jake, sorry if I'm not here but I'm out for the moment. I'll be right with you, have a beer in the meantime." Next to the note he found the glass of beer she referred to, and thirsty as he was he thirstily gulped it down, even if it did taste a bit odd. He didn't notice anything until he suddenly started sweating heavily, feeling like he was going to fall over. "Damn, I only had one beer...I can't possibly be drunk", he thought while his body hair was starting to drop off - though he didn't notice this. His well-defined muscles melted down to soft flesh, making his limbs much thinner than they used to be. "What's going on?!", he thought panickingly. His usual stout shape had become small and tubular, elegantly formed as a snake that never make any straight bends, all curves from neck to legs. His butt was stretching the back of his pants a bit as it became firm and round, his butt now much more defined and sticking out.
As his posture shrunk, so did his total size and he was now well over a foot shorter than he used to be, making his clothing way too big and it slumped over his shoulders a bit. Silky brown hair extended down his neck onto his shoulders, putting the last touch on an already petite face with thin eyebrows. Small bumps on his chest inflated beneath his shirt into significant hills that were even visible beneath a loose shirt, a B cup that was not all that big, but definitely firm. And now, the change had started that definitely marked his change of gender: his already shrunken member now definitely shrunk away, leaving nothing but the tip that reintegrated itself into the body as a clitoris. Beneath it the crotch had started folding inwards, surrounded by short black pubic hair.
She just sat there in shock at what just happened, white as a ghost and failing to comprehend it, though the first she managed to get out of her throat was a shrill soprano scream.