They perform some more magic tests and run out of mana and recover mana and perform more tests and a second sleepover could be fun but it's decided that people can do coordinated tests in their own places and there is not actually a need for them to all be in the same place. The Maxwells' driver takes Jess home (and Maya, too, if she prefers that to staying with the Maxwells but they assure her she's welcome to stay there), then takes Sadde, Theo, and Tyler to the Farron residence, where Sadde prefers to be dropped—he'll go to his place by public transportation, he'd like to talk to the—twins?—yes, thank you, it was a pleasure meeting you.
"Why don't I," offers Tyler. "You can try resurrecting me if I get torn to pieces, won't that be fun."
"And try bringing these with, I guess, so they can't freeze people to death."
… Right.
Off they go, then. Card-wards.
Theo checks periodically to make sure they're going the right way.
Okay, well, catch the ones nearby if he can but it's probably better to get to the source and stop it rather than trying to stem the flow, depending on how many of them there are.
Everyone agree?
Okay well Shadow can grab that one so it doesn't attack them, and they can continue following the invisible thing.
"Someone try a spell to see it?"
Scrolls, and: "The sun be my guide, the fire of my torch, light lead me and show me what's true, reveal what's hidden!"
There is a flash of eerie light, and the invisible thing is... revealed. In a way. It's more a presence than a visible thing, shaped like a rectangle if it can be said to have a shape.