Douglas Hill 
Blade of the Poisoner [EPUB ebook] 

Marked with the tainted sword of the evil Prince Mephtik, Jarral Gullen will die horribly unless both the blade and the prince are destroyed by the next full moon. With the help of his friends, Archer, Scythe and the Lady Mandragorina — a band of magically talented adventurers — Jarral undertakes a perilous journey to Mephtik’s demon-guarded fortress. Battling monsters and demons, they fight to overturn Jarral’s sentence of death.According to the wizard Cryl, only Jarral can save the country from Mephtik’s evil forces. Of the four friends, Jarral alone possesses the greatest magical talent. But will he live long enough to use it?