Osen

Osen was a Gardezzan scientist. She raised her son, Kaya, alone after the death of her bonded partner in the Dalek invasion.

Nius charged Osen with examining the Master's TARDIS, in the course of which one of her hands rapidly aged due to temporal energy. She became suspicious of claiming to be the Doctor when he produced his TARDIS key but ultimately helped him destroy the Dalek command ship and allowed him to dematerialise so that she would not leave her son orphaned.

In the TARDIS, Osen likened the Master to the Doctor and asked to be taken home. The Master instead tricked her into releasing the excess temporal energy, killing her. (AUDIO: Beneath the Viscoid)