When Cranleigh entered interstitial time as part of Jeremy Winterdawn's experiments, Gabriel and Tanith attacked his mind and used it as a blueprint, creating a revised mind from it. They then used the stuff of chaos of interstitial space, the building blocks of reality, to construct a body for the mind. The creature seemed perfect but the body structure was unstable, leaving defects. But the creature lived and became Harry Truman.
Justin went insane as a result, and some of his memories were blurred and covered by a mental block Gabriel and Tanith installed to be "an accident" to explain the loss. Several weeks later, Truman turned up at Shadowfell in response to an advertisement, being hated by Justin because he believed Truman had stolen his memories and identity, since both Justin and Harry were the same person. Because of this, Truman believed he had a twin sister (Nancy Cranleigh) who died three days after being born, and had been in love with a girl named Laura.
Believing he had been in an accident and that his face was scared and disgusting, Truman wore a wooden mask and was always worried it would fall off. He subsequently was in love with Sandra Winterdawn, as Justin was, and went into the interstix to videotape it for Professor Winterdawn, controlling the metahedron that opened the interstitial gap.
In reality, he had no face but just blank flesh. His mind shaped his face briefly, creating the scars he saw, and this allowed him to eat, talk, see, and kiss. If something such a knife was thrust at him, his flesh would part to allow the object, then fill in afterwards. Sandra actually revealed her feelings for him, seeing his blank face and finding it beautiful because it was "his face," and they were prepared to make love before Gabriel and Tanith entered and revealed his true nature. Tanith then told him she liked him before punching her fist through his head and dissolving his body, his mind-set being reabsorbed by Cranleigh. (PROSE: Falls the Shadow)