Logically, it's in the basement.

Right. You've been over most of the tower, and while you weren't explicitly looking for the summoning circle, it's not the sort of thing you'd have overlooked. Especially when it's occupied. Which means it's not in any of the three main floors. None of the side rooms were big enough to hold one, so you didn't have to go look through all of those, thankfully. So that leaves whats left of the fourth floor- or the roof- which is highly unlikely, as the bindings of a summoning circle are a tad bit fragile. Anything crossing the circle from the outside would break them, and while most animals preferred to avoid undead and outsiders, most was not all... and it most certainly didn't exclude flying debris, thrown objects, or just more of the tower collapsing. So that was out, at least for anything secure long-term.

Which meant it had to be in the basement. Not that you'd actually seen it or its entrance, but if your deductions are right, it's got to be there. So, the question is, where is it? You shake your head. You're not going to find it sitting around and wishing. If its' entrance is inside the tower, it's on the first floor. If it's not, it's on the grounds outside. Best get to work.

You groan as you move the last of the boxes off the trapdoor. Whoever owned the tower before the Shades- or possibly, whoever The Necromancers' Shade was before they degenerated- was relying more on subtlety then active defenses to keep people out of the basement. That or they just needed storage space and forgot about it. Either or. You sigh, and open the trapdoor. No sense in putting this off, really. A rank-one summoning circle wouldn't be able to hold anything more exciting then the outsider equivalents of The Necromancers Shade. Possibly a touch stronger, but still something you'd be quite capable of dealing with, especially as you're the Boss this time. Well, (Micro)Boss, but still. You descend the ladder and open the door at it's base, wincing at the groan of the hinges.

The circle is exactly where you predicted, glowing steadily. Of course, that pales in comparison to what- no, who- is in it. She- and you can tell she's female, given she's not wearing anything- is an utterly massive feline demon of some persuasion. She towers over you, having what you estimate is half again your height over you, and you're not short. It's not merely her height, either; each and every one of her muscles are defined and stand out against her skin, which when combined with her broad frame and massive breasts- Lyrissas' look like they're merely slightly above average in comparison- give her the impression of being some primordial titaness, which her four arms further emphasize.

"Well, aren't you cute," she literally purrs. "A fresh new necromancer, just having taken control of his first ruin after having driven out the local undead and bandits..." Her tongue flicks out, tasting the air like a snake before it withdraws, her lips twitching up into the beginnings of a smile. "... And uncovers the ancient evil within. So, young one... now what?"

You respond to her the only way you can think of... shaking your head, and shutting the door on her. "I am not dealing with this." You turn on your heel and head back up the ladder. You'll just have to do without Outsiders for now, probably by leveraging [Necromantic Overlord] somehow.