Complex sentence: Eventually, Ace not only discovers the connection that Finkle has with Einhorn, but also that they're the same person in a transgender disguise, implying that he may have killed Einhorn and underwent partial sex reassignment surgery to assume her identity.
Split into simpler sentences: Eventually, Ace not only discovers the connection that Finkle has with Einhorn, but also that they're the same person in a transgender disguise. This may infer that he may have killed Einhorn and underwent partial sex reassignment surgery to assume her identity.