Arthur was indeed hiding the truth from her. In his last attempt to glean something within, he saw the man sitting on the other side, waiting, calculating, and smiling. He found no soul, but a deep pit that led him to that man.
The man had short white hair, age lines covering his face, and a pair of white eyes with no pupils. It was the first time that Arthur met him, but no one could mistake him: the Father of Shon, Stealer of Bloodlines.
Rae would break down if she learned that her soul was somehow trapped or taken by the man that she loathed the most. The Father of Shon had created thousands of her kind from all over the theocracy and used them as weapons. He didn't want to tell her lest she do something extreme.
Before she pressed Arthur for the truth, which he would have to reveal anyway, Diana arrived to take him. She walked in and stared between the two, sensing that something was amiss.
"Am I interrupting something?" Diana asked.