"You guessed right. We have had them for hundreds of years in one form or another. No one else could have developed them here...only humans live in this world. Is it different on your world?" Adam answered and asked the alien.
That was how he would start thinking of her. It was obviously a 'her', it looked like a her at least, though he had no idea what the genders of her kind were. Or if they even had genders. But whatever she was, she wasn't human so she was an alien. Better then calling her creature or it.
"You will help us?" he asked. "We are prepared to compensate you for your services. Gold, jewels, magic...whatever it is that interests you."
Adam wanted to make sure she would help them before she let her out of the box, Pandora's Box so to speak. They didn't need two terrors marauding through D.C. There was something else she should know...
"Magical abilities won't work right until you are close to the demon. It is able to twist magic throughout the city except in it's immediate vicinity. Our witches can't cast their spells aboveground, so I am guessing you won't be able too. If it notices us, it can send out tentacles to crush us flat. There are also some contaminant it spurts out like piss from time to time. It carries an infection that reanimates corpses and turns them into berzerk zombies. They aren't like zombies in the movie...they are fast and strike without warning. This is where we come in. We will protect you till you are close enough to use your magic against the demon."