Flame and shadow seem the component parts of that lad's soul--no daylight in it, and no sunshine, and no pure, cool moonbeam ever shone there. He has an English frame, but, apparently, not an English mind--you would say, an Italian stiletto in a sheath of British workmanship. 
Flame and shadow make up that lad's soul, no English sunshine. You would say he is an Italian stiletto in a sheath of British workmanship. 