It had gone wrong. Horribly wrong. Maybe there was something that was overlooked when the treatment was first crafted, but this outbreak, this wasn't supposed to happen. It was up to you and your team to fix this, before the military couldn't contain this outbreak any more...
You were the youngest member of the research team, assigned towards researching a way to stop the transformations from happening, maybe even reverse it. It might have been why that large group of lizardpeople attacked your facility -- if they had caught wind of what you were doing of course they would try to stop you. It was chaos -- screams, growls, broken glass and gunfire when the soldiers assigned to guard you managed to get in and shoot down the intruders. But that wasn't before one of them got a hold of you, pinned you to a corner and roughly ripped at your clothes in an attempt to turn you so that you'd never pose a threat to them again; the bra holding your C-cups managed to remain intact but your panties got torn off. You did your best to fight them off -- you're not even sure whether it was a lizardman or lizardwoman who pinned you, chaotic as it was -- but you distinctly remember something disgustingly warm get into your mouth and something started going into your vagina before you heard the death screeches of your assailant falling to a hail of bullets. It was too late for you, though -- surely you were about to feel the reptilian changes overwhelm your body and mind and would about to join the lizardpeople.
...Unless. Your team had managed to develop an experimental trial antidote serum and had started producing samples for testing when the lizards attacked. On the lab bench next to you was a syringe already filled with the experimental serum. As soon as you realized your assailant was shot dead and you got your wits back, you managed to grab the syringe and stick it in your arm to inject it. You have no idea whether it would work, but the alternative was just to submit to becoming one of them -- if you were going to lose your body and mind, at least you'd do it trying to give humankind a chance at finding the answer.
The whole ordeal had exhausted you, even without the assault by whatever lizard attacked you -- the military soldiers who shot the lizards attacking you had moved on to clear the rest of the floor. Whatever happened the next few minutes, you'd be alone to witness.