The story takes place in an ordinary Japanese town, Fuyuki City. Hidden from society, there has been a deadly war going on in this town. Seven sorcerers known as "Masters" summon a powerful familiar called "Servants" and they all fight each other till the last one. The last one is said to attain the Holy Grail which will grant them a wish. Only a few knows when this War started and what the Holy Grail is, but the war was about to begin again this year.

The main character is Emiya Shirou, who lost his parents in a fire and was adopted by a man who called himself a sorcerer. Admiring his step father, he has been training himself to be a sorcerer. However, he had no talent and he could barely use one type of sorcery. His step father has already passed away, and today he's a sorcerer without any skills or knowledge. He is involved in the War of the Holy Grail when he accidentally summons Saber, who is said to be the strongest servant of all...

Based on "Unlimited Blade Works", the second part of the game.

From Wikipedia:
The Fate/stay night manga, illustrated by Nishiwaki Datto, began serialization in the manga magazine Shōnen Ace, published by Kadokawa Shoten, on December 26, 2005. It is an adaption of the Fate/stay night visual novel, rather than the anime. In contrast to the anime, the manga focuses solely on the Unlimited Blade Works scenario of the game, and has refrained from pooling story elements from the sister scenarios, Fate/hollow ataraxia or Fate/Zero. Currently, nine tankōbon have been released.