Hey!

Haven't seen you in a while. How ya been?
Yeah, you're probably right. The crystal did soak up the lux from the kit's night terrors. However, I should point out that his name is
Colin, not Conner. Dunno where you got that name, but it's not our little Questor fan.
Plus, he can't possibly be the only source. The wires probably go through a good part of the block, just under the level of the sewer lines so they wouldn't be discovered. Plus, lux is a form of energy, and it's possible Rosad Beither built that crystal to convert other forms into lux, like lightning for instance. That would explain why Mr. Millfolk thought Quentyn should pay close attention during a thunderstorm. He probably noticed that Colin tended to have the "night terrors" during those times. If the lightning strikes gave the crystal a good charge, that would explain why Colin saw the rats during those times. The rat king was able to pull off quite bit of lux and send a more sizeable army than usual. (Wouldn't be surprised to learn that some of these shadow rats tend to dissipate after a while, or at a certain distance.) A good theory so far; now to see if the evidence backs it up.
Quentyn really shines here. Dives right into their midst, swinging sword and torch, yelling at the top of his lungs. Gets buried, but quickly pushes back through, tossing off dozens of the little pests, struggling his way towards the rat king. Finally, having reached the place where the evil beast lay, ignoring the shadow rats nibbling on his ear and other parts, he lays into it with his sword, severing the tail and their connection, effectively killing it. The shock probably is what finished it; being disconnected from the four others was too much for any one of the rats.
His job done, the shadow rats fading into nothing, Quentyn kneels there, panting a little as he surveys his handiwork... then promptly slumps over for a nap.
"I think I'll just... lie here... bleeding quietly..."
*a strange little thing floats into the room and floats above our hero's head*
"Rest well, young Questor. You've saved the day, and help will be coming. Your sleep is earned. I can certainly see the stag was right about you."
*floats off, disappearing down the caverns just before the others arrive*
I'm lost. I've gone to find myself. If I should return before I get back, please ask me to wait. Thanks.