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While it is not clear whether or not he was a prisoner aboard the Astral Queen, Grimes vocalizes his support for Tom Zarek, espousing his belief that Zarek was a freedom fighter and hero. He is a part of the Sagittaron delegation that boards Cloud 9 with Valance, the suspected assassin targeting President Laura Roslin.
Grimes first gains the attention of Captain Lee Adama when Grimes tries to rough up a person who calls Zarek a murderer and terrorist. Later, Grimes attempts to assault the captain in a bar on Cloud 9, only to be subdued by Adama (with assistance from Kara Thrace).
During Adama and Thrace's interrogation of Valance, Adama claims that Grimes gave him up; it remains unknown whether or not there is any truth to this, given their "good cop, bad cop" interrogation routine on Valance. What happens to Grimes after the altercation remains unknown as well (Colonial Day).