Rachel was a human woman serving time in an underwater prison pod. At one point during her incarceration, she started bleeding, but there were no replies from the surface when the prisoners asked for help. She ended up recovering on her own.
Rachel had served two years of her ten year sentence when the Third Doctor and Jo Grant arrived in the pod. Like the other inmates, she was initially suspicious of them. The Doctor convinced her that he intended to get them out of the pod, though he wouldn't free them.