The third and final book of The Milkweed Triptych
Necessary Evil contains examples of:
- Alternate History: Another alternate history - an in-universe alternate timeline from the alternate history of Bitter Seeds. In this one, Gretel makes sure the war mostly plays out like in our history.
- Alternate Timeline: Gretel's plan was to create a timeline in which the Eidolons do not kill her or humanity.
- Go Mad from the Revelation: Gretel, when she realizes that she no longer has perfect control of the timeline.
- I Reject Your Reality: After 7000 heartbeats in close proximity to an Eidolon, Marsh2 starts losing his grip on how reality actually works.
- The Mole: Will becomes this for Marsh1 in Milkweed.
- My Future Self and Me: 2 × Raybould Marsh.
- Reality Warper: The Eidolons. Shown in detail when Will summons an Eidolon for Marsh2 in Berlin.
- Stable Time Loop: ... sort of. When Marsh1 tries to shoot Marsh2 in the knee and fails, their knee pain suddenly goes away.
- Time Travelers Are Spies: Marsh1 ends up in wartime London with another man's wallet and no period currency. Naturally, he's suspected of being a German spy.
- Trust Password: Needed to enter Milkweed. Fortunately for Marsh1, they're the same as in his timeline.