1984, Hong Kong. Seventeen-year-old Chen Mo is the most dazzling name of Aberdeen Technical School - he has won the mathematics competition for three consecutive years and is expected to be the top scorer in the 10 A-level examinations. He has climbed step by step from a tenement building on the edge of the Kowloon Walled City to the humble hope of the University of Hong Kong Medical School.
Until that September afternoon, Lin Guodong's Zippo lighter rang in his ear.
"Teach me math, and I'll keep you safe." A school bullying transaction replaced Euler's formula with club rules, and the calculus exercise book with a roster of horses. Chen Mo thought he was just taking a step on the edge of the cliff, but he didn't know that in the shadow of Taiping Mountain, every step was slipping - from copying people's ledgers to watching nightclubs, from the "parallel import mathematics" of smuggling watches to the precise packaging of white powder dealers. He used his talent for solving equations to calculate the survival probability of getting deeper and deeper, until one day he discovered that the young man who could see through all theorems at a glance could no longer calculate how much he had left to lose.
And when he finally stood on the highest rooftop of Victoria Harbor, holding in his hand a ledger that could overturn the entire group, with swordsmen chasing him behind him, and in front of him the Star Ferry crossing the sea - Chen Mo suddenly remembered a problem he had solved when he was seventeen: the height and time of a free fall, h=½gt². It takes 7.8 Seconds to get from the Victoria Peak Observation Deck to the ground.
In those seven point eight seconds, he could have thought of his mother's tape-covered fingers, of the lemon-scented ponytail in the library, and of all the other lives that should have belonged to him.
