When his younger sister's mechanical heart suddenly began playing a countdown to the apocalypse, grassroots mechanic Cai Maocai discovered that the Federation-standard heart implanted after the "car accident" three years ago was actually a doomsday spark from an ancient civilization. To stop the countdown from reaching zero, he had to navigate the Star-Ring Sisterhood's pursuit and the Rust-Iron Brotherhood's tempting offers. But he soon realized that every mystery he unraveled made Xiaoyu's heartbeat speed up. Save his beloved sister or save humanity? It was the cruelest mechanical dilemma of all.
