Le feu écarlate (Thorgal, #35)

Thorgal has failed. Despite all his efforts, he wasn’t in time to
save his son Aniel, and was forced to look on as sorcery transformed
the young, mute boy into a teenager with terrible powers – the
reincarnation of the Master of Red Magic. The Viking, convinced there
is still a chance, is still not ready to give up. But many threats
are converging, from within the city and from afar, and the stakes
may be much higher than he imagines …