The first place Scott and you check is the library. But after only ten or fifteen minutes, he throws his hands up with a snarl. "It’s not here!"
"It must be somewhere in here", you say. "Like in the movies."
"We're wasting our time."
"You can start checking out the rest of the house," you tell him. "I'll keep looking in here. Like, maybe there's a secret room?" You start pulling out books and feeling at the shelves behind. Your nerves are being frayed by the arrhythmic tics of two nearby grandfather clocks.
Scott looks around with his hands on his hips, then points at a wall.
"There," he says. "That basement where we found Lucy. It'll be on the other side of those shelves. Maybe the secret door is there?"
You feel your eyes light up, and you hop over to join him. 
"Dur! You're right! Are there any candlesticks to pull?" That's the way it's done in the movies, after all. In fact, there aren't any candlesticks, but there's a small stuffed dog—with a couple of heads—sitting in a nearby alcove, and when Scott lifts it, one of the shelves clicks and falls open, like a heavy door. You and Scott exchange bright grins as you pull it open, and grip your crowbars tightly.
On the other side is the cellar, and the top of the spiral staircase. You and Scott crowd in but don't descend. He shines a flashlight over the barren space within. The broken window, you notice has been sealed up with a sheet of plywood. Unless there's another secret passage down there, it's a dead end.
--
You make a search of the lower rooms—kitchen, dining room, a sitting room and a living room—before moving upstairs. At the turning of the staircase, you both pause at the sound of pattering feet in the upstairs hall. You look at each other, the same puzzlement knitting your brows. The tread is far too light to be the fat professor's; and it sounds like there's more than one pair of feet. If you didn't know better, you'd swear it was the sound of three or four children running down a carpeted hallway. You creep to the top, and peer around the corner down the hall. It is empty, and all the doors, save the one into the bedroom you entered the house through, are shut.
You tackle the professor's bedroom first, searching everywhere—under pillows, the mattress, between the sheets of the bed; inside every drawer and under every folded piece of clothing. Scott taps at the walls, and when he excitedly yelps that he's found a hollow space behind one of the panels, you pull at every protuberance on the wall. None of them open anything, and in his frustration Scott snaps off a wooden arm that looks like a candle-holder.
"Calm down, man!" You can’t believe that you’re less nervous than him. "We've got the rest of the floor to check out! Let's try the room on the other side."
It's completely bare, though, and tap as he does, Scott can't find that hollow space again. He returns to the master bedroom for another search while you move through the other rooms on the upper floor. One is an office, which causes your heart to leap with hope, but it proves a bust as well, even after Scott rejoins you to make the search. The others are bedrooms much more stark and bare, and easily searched. But in one of these, furnished only with a small bed and an armoire, you at last turn up something of interest and use: a mask like the one you made, and a small metal strip covered in what look like Norse runes. Cheered by the discovery, you and Scott make a hard search for anything that might be a secret panel, but turn up nothing.
Out in the hallway, you look down toward the last place to explore: a narrow staircase at the back of the house. At the top you find a small loft. It has been furnished as a kind of workroom, with a work table, a pegboard hung with tools and instruments, and a small plastic tool chest with lots of little drawers. Scott looks through these, muttering to himself, as you study the pegboard. You've never taken a shop class, and you've never paid attention to the tools your dad keeps in the garage, but you're struck by the fact that there's nothing hanging there that resembles a hammer, a screwdriver, a saw, or any of the other implements you'd expect. Everything has an odd shape: awls shaped like corkscrews; a set of goggles with three lenses; a thing that looks like an astrolabe. The table itself is etched with strange symbols, some resembling runes, others in a flowing script that could be Arabic, Hebrew, or Indian.
It all makes your scalp prickle. This is a workroom. It's a workroom where occult things are done.
Your hunch is vindicated when you spot a bag of quicklime under the table. "This is it," you tell Scott, and point at the bag. "That's some of the stuff you use to make masks. Ooooh!" You leap for a small cupboard that you had overlooked before, and wrench the doors open. The book has to be in there!
But it isn't, and you have to bite down on your cry of disappointment. It's a supply cupboard, packed with a lot of small tubs of powders and liquids and pastes, each one labeled with an inscrutable symbol. But there's also a stack of papers, and hard-bound writing notebook. You pull these out and spread them over the work table. You and Scott crowd together to study the sheets, which are covered in a flowing script. 
As Scott shuffles through the papers, you open the notebook. It is filled with cryptic notes in the same flowing script — Blackwell's handwriting? — and scribbled doodles that remind you of the symbols — sigils, the professor insists — that were contained in the book. You feel a rush of blood to your head as your intuition takes over, and with mounting excitement you pore carefully over the first page, then the second, then the third.
The notebook is describing the contents of the Libra Personae! It's all there! A description of a sigil that requires an offering of blood; a description of a mixing and firing process, as when you made the mask. You can't decipher the list of ingredients — they are written in a chemical notation — but there's no mistaking the meaning.
Greedily, you flip pages, and note that at the bottom of each, in block letters, is a single word or phrase that you guess summarizes or describes each spell: PERSONA, EMPLASTRUM, MENS, GLUTEN, PEDISEQUOS, CADAVER, SERVUS.
"Well, this is a waste," Scott mutters. "I can't figure any of this out."
"These are his notes," you reply.
"I get that!" he snaps. "Fucking useless without the book, though."
"It's better than nothing."
Scott looks dubious, and moves to open a door on the other side of the loft. It leads to another room, only the size of a closet, with a skylight and a floor-length mirror. He tries pulling the latter off the wall, and runs his fingers around it, as though searching for a latch.
You, meanwhile, start gathering up all the notes and all the materials. "What are you doing?" Scott asks.
"Cleaning him out," you say. "If he hasn't got the shit to make his masks, that's a win all by itself."
"He can just buy some more."
"You don't know that! Maybe some of this stuff is really rare. Even if he does, it'll delay him." You start pulling tools down off the pegboard. "We need to fuck him up any way we can."
"That book is what we need!"
"I know that, man! But we need to clean him out before he gets back."
Scott makes no move to help you, though, and with a snarl of frustration you gather up everything you can in your arms and take it downstairs, where you dump it onto the dining room table. You make a fast search of the kitchen for a couple of garbage bags, and run back upstairs to sack up as much as you can. You don't pass Scott on the way back up, but he's gone from the workroom when you get back, and you cuss to yourself over his pigheadedness as you shove tools, supplies, notes, and every loose bit of whatnot you can into the trash bags.
Downstairs again, you pack up the rest of your stuff and move it to the front door before going back inside to look for Scott. You find him in the library, pulling at shelves. "We need to go," you tell him.
"Not without the books."
"No! Now!"
Scott gives you a pale, wild-eyed look, then moves over to the secret door into the basement. "We should check down there," he says.