“Yes, but what if they came in another way?” The spren she’d interviewed claimed that the Masked Ones—Fused with Lightweaving powers—couldn’t enter the tower. Its ancient protections had some lingering effects, like the changes in pressure or the warmth. Indeed, this seemed proven, as while Masked Ones sometimes slipped into human camps, they had never come to Urithiru.

At least so far as Navani could tell. Perhaps they’d just been very careful. “The enemy,” Navani said to Rushu, “has abilities we can only guess at—and the powers we do know about are dangerous enough. Masked Ones could be among us and we’d never know it. You or I could be one of them right now.”

“That … is a highly disturbing thought, Brightness,” Rushu said. “What could we possibly do? Other than fixing the tower’s defenses.”

“Gather a team of our best abstract thinkers. Assign them the task of creating protocols to identify hidden Fused.”

“Understood,” Rushu said. “Dali would be perfect for that. Oh, and Sebasinar, and…” She slowed, pulling out her notebook, oblivious to how she was standing in the middle of the corridor, forcing people to step around her.

Navani smiled fondly, but left Rushu to her task, instead turning right and entering one of the ancient “library” rooms. When first studying the tower, they’d found dozens of gemstones in this room, all encoded with short messages from the ancient Knights Radiant.

Over the months, the room had transformed from a dedicated study of those gemstones into a laboratory where Navani had organized her finest engineers. She had been around enough intelligent people to know they worked best in an encouraging environment where study and discovery were rewarded.

Inside this room, concentrationspren moved like ripples in the sky, and a few logicspren—like little stormclouds—hovered in the air. Engineers worked on dozens of projects: some practical designs, others more fanciful.

As soon as she stepped in, an excited young engineer scrambled up. “Brightness!” he said. “It’s working!”

“That’s wonderful,” she said, struggling to remember his name. Young, bald, barely a beard to speak of. What project had he been on?

He grabbed her by the arm and towed her to the side, ignoring propriety. She didn’t mind. It was a mark of pride to her that so many of the engineers forgot she was anything other than the person who funded their projects.

She spotted Falilar at the worktable, and that jogged her memory. The young ardent was his nephew, Tomor, a darkeyed youth who wanted to follow his uncle’s path of scholarship. She’d assigned the two one of her more serious designs, a set of new lifts that worked on the same principle as the flying platform.

“Brightness,” Falilar said, bowing to her. “The design requires a great deal more tweaking. I fear it’s going to require too much manpower to be efficient.”

“But it’s working?” Navani said.

“Yes!” Tomor said, bringing her a device shaped like a jewelry box, around six inches square, with a handle on one side. The handle—like the one you might use to pull open a drawer—held a trigger for the index finger on the inside. A button on the top was the box’s only other feature, except for a set of straps that she took for a wrist brace.

Navani accepted the box and peeked in through the access panel. There were two separate fabrial constructions inside. One she recognized for a simple conjoining ruby, like those used in spanreeds. The other was more experimental, a practical application of the designs she’d given Tomor and Falilar: a device for redirecting force, and for quickly engaging or disengaging alignment with the conjoined fabrial.

It wasn’t exactly the same method that kept the Fourth Bridge flying. It was more a cousin to that technology.

“We decided to make the prototype an individual device,” Falilar said, “as you wanted something portable.”

“Here!” Tomor said. “Let me get the workers ready!” He scrambled over to a couple of soldiers at the side of the room, assigned to run errands for the engineers. Tomor got them into position holding a rope, like they were about to engage in a tug-of-war—only instead of a rival team on the other end, their rope was attached to a different fabrial box on the floor.

“Go ahead, Brightness!” Tomor said. “Point your box to the side, then conjoin the rubies!”

Navani strapped the device to her wrist, then swung her arm around, pointing it to the side. Right now, the rubies weren’t conjoined, allowing the box to move freely. Once she pressed the button, however, the device snapped into conjoinment with the second box, the one on the floor attached to the rope.

Next, she pulled the trigger with her index finger. This made the ruby flash brightly for the soldiers, who began pulling their rope. They moved their box along the floor, and the force was transferred across the space to Navani. And she was yanked—by the box and handle strapped to her wrist—steadily across the room.

It was a common application of conjoined fabrials. The big difference here was not in the fact that force was being transferred, but the direction of the transfer. The men were pulling the box backward along the wall, moving steadily eastward. Navani was being pulled forward along the axis where she’d pointed her arm—a random direction south by southwest.

She flashed the light to warn the soldiers, then disjoined the fabrials, so she stopped skidding. The men were ready for this, and prepared as she pointed her hand in a different direction. When she conjoined again and flashed the ruby for the men, they began pulling—and she moved that way instead.

“It’s working wonderfully,” Navani said, skidding on her heels. “The ability to redirect the force in any direction—on the fly—is going to have huge practical applications.”

“Yes, Brightness,” Falilar said, walking beside her, “I agree—but the manpower issue is a serious one. It already requires the work of hundreds to keep the Fourth Bridge in the air and moving. How many more can we spare?”

Fortunately, that was the exact problem Navani had been trying to solve. This is working, she thought with excitement, turning off the fabrial, then having the men pull her in a third direction. Making the Fourth Bridge rise into the air had not been terribly difficult—the truly hard part had been getting it to move laterally after raising it into the air.

The secret to making the Fourth Bridge fly—and to making this handheld device work—involved a rare metal called aluminum. It was what the Fused used for weapons that could block Shardblades, but the metal didn’t just interfere with Shardblades—it interfered with all kinds of Stormlight mechanics. Interactions with it during the expedition into Aimia earlier in the year had led Navani to order experiments, and Falilar himself had made the breakthrough.

The trick was to use a specific fabrial cage, made from aluminum, around the conjoined rubies. The details were complicated, but with the proper caging, an artifabrian could make a conjoined ruby ignore motion made by the other along specific vectors or planes. So, in application, the Fourth Bridge could use two different dummy ships to move. One to go up and down, the other to go laterally.

The complexities of that excited Navani and her engineers, and had led to the new device she now wore. She could move her arm in any direction she wanted, conjoin the fabrial, then direct force through it in a specific direction.