Taiwan's Matsu islands head into a two-man race for county magistrate, and a corruption investigation has turned what looked like a safe win into a toss-up.

• Incumbent KMT magistrate Wang Chung-ming faces independent challenger Tsao Erh-yuan, a former land administration chief.
• Wang looked like the favorite thanks to four years of local groundwork and the resources that come with holding office.
• A corruption probe into lawmaker Chen Hsueh-sheng has shaken the deep-rooted local political networks and lifted Tsao's chances.
• Matsu votes on personal ties — same school, village, clan, surname, temple — more than on party, which is why the DPP has repeatedly lost there and is sitting this one out.
• Matsu natives living and working in New Taipei and Taoyuan hold enough votes to decide the result.

Outlook: The race is wide open, and how far the corruption case spreads — plus which side the DPP quietly backs — will likely decide it.