SINGAPORE — When author Seo Mi-ae came home from a college hiking trip with a cut on her face, it took her family three days to notice, even though they had shared meals and lived under the same roof the whole time. The Korean thriller writer still uses that small lapse to explain how her genre works. In crime fiction, a sentence skimmed in passing or a figure lingering in the background can turn out to matter most. That idea runs through Seo’s psychological thrillers, and it is also the theme of this year’s Singapore Writers Festival (SWF), “Hidden in Plain Sight,” which opened Friday. Seo is one of the featured writers in the festival’s new Crime and Mystery Spotlight. Often called the "queen of mystery," Seo, 61, is one of the country's best-known thriller writers. She started her career in 1994, when her short story "30 Ways to Kill Your Husband" won a spring literary contest. Several of her works have since been adapted into TV dramas, films and plays. Her 2010 novel "The Only Child" follows a criminal psychologist summoned by a serial killer on death row. It has been s