Author's Note : My first Doctor Who fic, please be kind!

Koschei and the Master are very different. So very different one may find it unbelievable that they were ever the same. However, there is one thing Koschei and the Master have in common. They both want to keep their Theta.

From the first moment Koschei set eyes on Theta, he wanted him. Theta, so bright-eyed. Theta, so spirited and smart. Everyday after their meeting Koschei found himself fearing for the innocence of his little Lungbarrow. He feared that the horrors of such an ever-changing universe would snatch it away, as wind moving the silver leaves. He wanted, needed to keep Theta safe. He must always be safe from the outside. He would keep the younger boy beside him always, chain them together so that he could always protect Theta from a universe that would swallow him whole. In a cage, soft, strong, and made out of love he kept his Theta Sigma. Soft words, gentle touches and passionate loving always present to reassure his younger lover that this is where he should be. Safe in Koschei's arms. Safe, where Koschei would never, ever let any harm come to him.

So, Theta stayed.

So many centuries and fights and hurts and losses later, Koschei is very much dead. The Master, however, is not. He is selfish, he is greedy, he is insane, and although the love Koschei had for Theta died with him, his desire remains. Theta had seen so much and lost even more, there is not much left in need of protecting. Not that the Master would bother. He doesn't serve Theta, Theta serves him. He takes his Theta, bullies him, dominates him. His cage is strong as steel and built of lust, with not a spare centimeter for his Theta to fly. Rough taction, skin bruised by teeth, and more often than not violence keeps the Master's little Timelord knowing his place. Because there is nothing beyond this for him. He has only this violence and desperate need and cruel fingers scratching "mine" into his skin in the dark of night. The Master will take what he wants and give back to his Theta only what he sees fit. Because Theta is his. He always has been, always will be. They both know that Theta has nothing. No home, no family, no Koschei to protect him from the evil who holds his almost like lover.

So, Theta stays.