Sequel to Blindsight.

Wikipedia:

Echopraxia is a hard science fiction novel by Canadian writer Peter Watts. It is a "sidequel" to his 2006 novel, Blindsight, and the two novels make up the Firefall series.

Echopraxia follows the story of a biologist who gets caught up in a voyage into the heart of the Solar System among members of a transcendentalist monastic order and allies (including a vampire escaped from a research facility and her cadre of zombified soldiers) to investigate a mysterious signal seemingly coming from the mission sent to initiate first contact in Watts' previous novel.

The title refers to a psychological condition in which a person involuntarily mimics actions they observe.

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