Yoshiaki Maeda and Yuuko Nishikawa were colleagues at the same company. Being equal and holding the same position, Yoshiaki began to have secret feelings for Yuuko.
But she herself had fallen for a subordinate, and they got married.

Yoshiaki's hopes didn't die with the knowledge of that fact.He watched the newlyweds flirt and make out at work. He plotted and fantasized that Yoshiaki was his. She would be his someday still. Then when his thoughts could get no darker, the chance came to act.

[From DLsite English]