The Resonant Kill. THE ECHO TRACERS, #3

The "Silence" has been broken. After the high-level exposures in D. C., a brilliant but unhinged former government contractor-the man who originally designed the "Echo-Mapping" technology-goes rogue. He believes the technology should be a weapon of mass control, and he's ready to prove it. He unleashes a "Sonic Virus": a specific, oscillating frequency transmitted through the city's emergency alert systems.
It's not just noise; it's a resonant frequency designed to shatter glass, disrupt the inner ear of anyone in range, and cause mass structural failure in the city's aging infrastructure. As D. C. descends into a literal state of vibration, Maren and Agent Elias Vance are the only ones who can triangulate the broadcast source. But the villain is using Maren's own specialty against her, creating "acoustic mirrors" that make his location impossible to pin down.
In a high-stakes finale, they must track the signal into the city's deep underground-the subway tunnels where sound bounces and multiplies in a deadly maze.