He called Mira. “Chapter 12’s last problem. Who submitted it?”

“I wrote the first volume’s answer key,” Aris said flatly.

The Last Equation

A GRB. Not a natural one. The light curve was too perfect: sharp rise, exponential decay, then a second peak exactly 0.73 seconds later. And embedded in the high-energy tail, a new message.

The last problem was typed in a font no one else seemed to notice—a perfect match for Lena’s old terminal.