AT SIX THAT EVENING, AS THE DAY DREW TO A CLOSE AND THE SHADOWS fell over Ellingham, Stevie Bell stood in her room, tucking herself into the suit that still smelled strongly of mothballs and must from the costume attic. She stood before the mirror and did what the famously fastidious Belgian detective would do—she adjusted her mustache until it was perfect. She tucked a pillow into her front to fill out her belly a bit and take up some of the extra space in the baggy suit. She’d found a walking-stick prop and some white gloves, and the overall effect was pleasing.

This tunnel stuff was stupid. If there was a tunnel under Minerva, someone would have found it by now. David. Ellie. Someone. It would have loomed large in the legend.

Still, a passable effort would need to be made. Hercule would look.

The source of the tunnel would have to be on the first floor. This meant the possible entry points were the kitchen, the common room, the hallway, either one of the two bathrooms, or any of the three bedrooms. She had already crawled all over Ellie’s floor. There was no evidence of a tunnel in there. Of course, entrances could be carefully hidden, but still. She got down and examined her floor, crawling, tapping, picking at the boards. Nothing.

She could check Janelle’s room later. Janelle was deep into her Wonder Woman transformation and could not be disturbed. But it seemed unlikely that the bedrooms were the source. The entry would have to be through the floor.

She went to the kitchen, poking into the back of the cabinets with her stick. It was possible the refrigerator or the stove or dishwasher could have been covering the opening, but then, surely these spots had been checked. You needed to hook these things up with water and gas. The refrigerator was heavy. A hollow spot under it would likely have been found.

She walked around the common room, looking at the flagstone floor. This was a more promising area, as any one of these stones could be a hatch. But it certainly appeared that the seals were tight. Similarly, the bathrooms showed no sign of having a passage anywhere in the floor.

It was a perfunctory check, and she would look more later, but it really seemed that Fenton had to be wrong. Maybe there was a tunnel somewhere on the campus that had not been found, but it probably wasn’t here.

She was crawling down the hallway, examining the boards, when Nate came up behind her.

“What are you doing?” he asked.

Stevie stood up and adjusted her pillow stomach.

“Nothing,” she said. “Thought I dropped something. Is that your costume?”

Nate was wearing his normal clothes—his grayed-out cords and a loose T-shirt.

“I don’t do costumes,” he said.

Janelle’s door swung open, and Wonder Janelle stood in the doorway.

“You think you’re getting away with that?” she said to Nate. “I guessed this was going to happen.”

She reached behind her door and plucked out a long gray cloak made of some coarse material, a wizard hat of a similar color, and a gray beard. She extended the outfit in his direction.

Nate stared and did not move.

“You just . . . had that there?” he asked.

“EBay,” she said. “And a little sewing. Take it.”

Nate took the costume and put it over his arm.

“And here.”

She reached back again and produced a tree branch that had been roughly fashioned into a staff.

“How . . .” he said.

“Listen to me,” Janelle said. “A lot of bad things have happened this year. It’s been scary and sad and horrible. But we’re here, and this is a holiday, which means we are going to celebrate because not everyone from this house can do that. So put on this wizard stuff, let me fix my tiara, and we go.”

She shut her door.

“She’s had this,” Nate said. “All along.”

“She’s Janelle. She can see around corners. Are you going to wear it?”

Nate felt the material between his fingers, then picked up the staff and examined it.

“It’s a pretty good Gandalf outfit,” he said. “I guess she made this staff? Like she went out and found a branch?”

“Because she’s Janelle,” Stevie said.

They went to the common room and Nate started to slip into the robes. There was the creak of footsteps moving overhead. Janelle stepped out of her room, her tiara now perfectly in place, with a round shield on her back and a sword in her hand. She regarded Nate with a satisfied nod.

“Good,” she said. “Team Minerva. Where’s David?”

There was a patter of steps and the ungodly creak of the stairs, then, out of the dark of the hall, he emerged.

“Oh,” Janelle said. “That’s . . .”

“You did the . . .” The words were dying in Stevie’s mouth. “. . . Sherlock thing.”

David had, in fact, done the Sherlock thing that Stevie had dismissed for herself, specifically, the BBC one. He was wearing a sharply cut blue dress shirt, slender, tailored pants, and a long gray-black coat with a red interior. He had teased out his hair a bit and made sure it curled. In many ways, it was a perfect costume while not being a costume at all. And it was obviously intentional, directed at her.

Stevie’s legs decided to debone themselves and her body became a hormonal swamp. She clutched her pillow belly for emotional support.

“What are you?” he said to Stevie. “A . . . chef?”

“She’s Hercule Poirot,” Janelle said, as if it was obvious that the baggy suit and fake mustache also translated.

“And Wonder Woman! And Gandalf! And Sherlock! All together! Just like nature intended. Should we go?”

The four of them headed out into the night. They were met on the path by Vi, who was dressed as a perfect Steve Trevor.

“So,” David said as the five of them passed under the dark trees to the Great House. “Is this weird?”

“Which part?” Stevie said.

“Is there fan-fic of this? You know, these two. What does that look like? What do we call it? Porlock? Sheriot?”

Janelle and Vi were arm in arm, Wonder Woman and Steve. Nate was off by himself, his cape brushing the lawn.

“Where did you get the coat?” Stevie said, trying to sound casual.

“What, this old thing?” he said, extending his hands in the pockets and showing it off. “I just charged a two-thousand-dollar coat to my dad’s credit card.”

“There are two-thousand-dollar coats?” Stevie replied.

“He’d want me to have it. I can’t look shabby, can I? Not at the White House.”

This was the first time David had ever said anything about his father’s ambitions, and Stevie glanced around nervously.

“They didn’t hear,” he said. “And wouldn’t understand if they did.”

They walked in silence for a moment. The world was spinning gently as she comprehended what was going on—he was doing the sexy dress for her. Not the other way around. He was trying so hard, reaching for her.

“No chance you know about any tunnels under Minerva?” she asked, trying to regain some composure.

“There are no tunnels under Minerva.”

“Not according to Fenton.”

“What is a Fenton?”

“Fenton is the professor I work for in Burlington. The one writing a book about the case.”

“There are no tunnels under Minerva,” he repeated. “You think I wouldn’t notice a tunnel under Minerva?”

“Secret tunnel,” she said.

“I repeat.”

“She seems pretty sure.”

“Well, I’m pretty sure too. You haven’t said if you like my coat.”

“I like your coat.” She meant it to come out dry and unaffected, but instead her bastard throat betrayed her with a tiny croaking sound on the last syllable. The body was the enemy of the mind.

Ellingham had gone all-out for the Halloween party. The Great House was made for occasions such as this, quite literally. All the overhead lights had been turned off and illumination came in the form of hundreds of tiny flickering electric candles. They were on every surface and lined the staircase. The diffused light winked off the crystal. A fire roared in the big fireplace, where a s’mores station had been set up, manned by Kaz, who was dressed as David Bowie, with a lightning bolt across his face. Call Me Charles approached dressed as Charlie Chaplin.

“You guys ready for some fun?” he asked.

“No,” David said.

Charles let this slide and pointed toward the door of the ballroom with his costume cane.

This was not a silent party tonight. The ballroom, with its mirrored walls and its carnival mask decorations, flickered with light and was rich with sound. There were orange and white fairy lights draped from the ceiling, and hundreds more tiny electric candles flicking along the walls and floor. A table was set up with drinks and snacks. A few regular suspects were in the middle of the floor, dancing away, including Maris, who was wearing a red flapper outfit, a choice that felt inevitable to Stevie. Dash was there as well, dressed as Han Solo. Vi extended a gallant hand to Janelle, who took it. Wonder Woman and Steve began to dance.

“Hey.”

Mudge was standing next to them, dressed as Mickey Mouse. A six-foot-five Mickey Mouse, with big ears coming off his jet-black hair.

“Cool Gandalf,” he said to Nate. He looked a bit more confused by Stevie and David, but nodded politely.

“I’m a watch ad,” David said. “She’s a hipster grandpa. Together, we solve crime.”

Mudge cocked his head at this and decided his time might be better spent elsewhere. Nate also looked around the room from under the massive brim of his wizard hat and immediately decided that he was going to the s’mores station. Stevie and David were left standing on the side.

“You want to dance, Grandpa?” he asked Stevie.

“Hercule.”