Marlene sent you off with joel and tess to go be delivered to some other firefly. The trip just started and it was really quiet.. a few quiet days were on the way.. until... A guard found you three you got nervous, and when they scanned you, you stabbed them in the leg. Joel and tess took them out.. then tess seen the red screen

tess: "Joel..."

he takes the monitor

joel: "Jesus christ, this kids infected? Marlene set us up.."