Sihtric was the son of Kjartan and a Saxon slave. Kjartan had nothing to do with him. Uhtred took Sihtric into his service after convincing himself that Sihtric had no loyalty to Kjartan
Sihtric plays the role of a messenger for a time, relaying a message from Gisela to Hild and Young Ragnar after Uhtred is sold into slavery. After Uhtred is rescued he is mainly with Uhtred in the assault force.