Namatay si Mayor Dacanay sa mismong araw na pinarangalang Junior Detectives sina Uno, Junior, at Thirdy sa bayan ng Valenciano. Natagpuan ang Mayor sa opisina niya, sarado ang mga bintana at pinto. Walang puwedeng daanan ang suspek. Para kina Uno, Junior, at Thirdy, iisa lamang ang maaaring salarin.
May isang sekretaryang nakulong; may isang anak na naulila; at may magkakaibigang lulutas sa kaso ng closed-door mystery.
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Mayor Dacanay died on the same day that Uno, Junior, and Thirdy were named Junior Detectives in the town of Valenciano. The Mayor was found in his office, with the windows and doors closed. There was no way the suspect could have entered. For Uno, Junior, and Thirdy, there could only be one killer.
A secretary is jailed, a daughter is orphaned, and a group of friends set out to solve the case of the closed-door mystery.
