A string of murders with dead female victims with short hair and glasses leads Birdy to investigate them with Tsutomu. The culprit is revealed to be a rogue combat marionette, which is killing the victims as it thinks of them as the mother, the main programmer when the marionette was placed under her care. Birdy attempts to retrieve it, but is attacked by supposedly a Federation-based person with a guardian robot that attacks her to keep her away from acquiring the disabled robot.

地下鉄構内で連続殺人事件が起きた。その事件が起こる時には、近隣のラジオやテレビから「呪いの歌」が聞こえてくる…という噂が流れていた。一方、バーディーも一連の事件に地球人以外が関与していると直感し、捜査に飛び出す。が、しおんの姿で自宅を出ようとした矢先、つとむの姉であるはづみが帰ってきてしまい…。