The bathroom was an almost perfect place; his living room was too exposed even when the curtains were closed and the bedroom was too cluttered for him to concentrate.

Oh, the bathroom had its flaws, true. The lights over the sink buzzed and hummed like a cloud of flies on a dead animal in a field. Eventually, he’d removed four of the five bulbs—the electric roar was less offensive, but it left things dim and he worried about what might be hiding in the corners and behind the toilet. Still, if he had to choose, speed must come before security.

And the tiles in the shower were ideal for his work: he could work on the math and substitutions using dry-erase markers, wiping away errors with bits of toilet paper, and when that ran out, the heels of his palms. The day before he broke the lock on the outer door to his apartment, he’d stealthily ventured out and bought dozens of eight-packs of the markers, stocking up. The tiles were now covered in ciphers, codes, runes, script—the subtle math of the damned.