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Under Colonel Kendra Shaw and Captain Kara Thrace, she leads a team of Marines that boards a Cylon basestar in order to rescue a captured Raptor crew. When the arming mechanism of their nuclear weapon fails, she prepares a manual switch that Shaw uses to detonate the bomb (TRS: "Razor").
During the occupation of New Caprica, Mathias leads Sharon Agathon's Marine escort on the planet as part of Admiral William Adama's rescue operation (TRS: "Exodus, Part I"). She and her team repel a Cylon ambush of a preliminary meeting between Agathon and the New Caprica Resistance under Samuel Anders. She then accompanies the group back to New Caprica City to discuss the rescue plan with the resistance leaders (TRS: "Exodus, Part I"). When Adama's plans are executed, Mathias is placed in charge of the Marines participating n the attack on the New Caprica Detention Center (TRS: "Exodus, Part II").
Following the evacuation of New Caprica, Mathias is involved in a number of key actions. She joins a boarding party that investigates an infected basestar discovered at the Lion's Head Nebula. She is assigned to execute prisoners retrieved from this baseship in a failed plan to infect the entire Cylon race via the download process (TRS: "A Measure of Salvation"). She also leads the Marine force on the so-called algae planet and is ordered by Lee Adama to detain Samuel Anders when he attempts to rescue his wife (TRS: "The Eye of Jupiter"). When Kara Thrace takes President Laura Roslin hostage, Mathias commands the Marine response team and escorts Thrace to the Galactica hangar deck after she is released from the brig (TRS: "Six of One").
Mathias is selected to join Demetrius on its mission to find Earth under the command of Thrace. Two months into the mission, she dies during an extravehicular inspection of a damaged Heavy Raider when its reactor explodes (TRS: "The Road Less Traveled").