The episode narrows the focus to five people close to the family—Serika Wakamatsu, Masashige Shiina, Sumio Fujinami, Yoshimi Satake, and Sakurako Yonehara—all of whom have an "S" in their name, matching a clue in the dying message. Key Plot Developments
Powdered poison is discovered on Ikuro's doorknob and Serika's slippers, initially framing her for the crime. Detective Conan Episode 653
The investigation takes a darker turn when Serika Wakamatsu is herself found dead in her office from cyanide poisoning at the end of the episode. The episode narrows the focus to five people
, titled "The Design of Poison and Mirage (S)" , is the second part of a four-episode story arc that aired on April 21, 2012. This episode continues the "Illusion" case, featuring a collaboration between Conan Edogawa and his rival/friend from the West, Heiji Hattori . Case Overview Location: The Wakamatsu family residence in Tokyo. , titled "The Design of Poison and Mirage
This arc is notable for the early appearances of Masumi Sera , who continues to observe Conan’s detective skills. The Design of Poison and Mirage - Detective Conan Wiki