Krey pariah turned into a living bomb. Karkar chose to rebel against the scientific experimentation on his family (which they signed up for). As a result Karkar was first exiled and then returned home to discover his parents have had their minds wiped of memories of him.
Now Karkar has three days to negotiate peace or he will be forced to destroy the planet and himself. He is also highly aware of the fact that if he does negotiate peace between the Krey and the Sceeeee he will still be killed since removing the bomb is impossible.