"A squire approaches you and hands you a spotless suit of Plate Mail. "It belonged to my master," he says angrily, "but he fled the battlefield at the first sign of danger, shaming himself as well as me!""
The Plate Mail is an artifact from Heroes of Might and Magic IV that gives heroes +10 melee and ranged defense, but reduces their in-combat movement by two, and makes their spells cost two more mana. It costs 1000 gold from a blacksmith.
It is very similar to the Chain Mail the bonus is bigger but so are the annoying side-effects. The defense increase can be a life-saver in the first few weeks of the game if worn by a magic hero, but sadly it makes the casting of even the simplest spells expensive. Might heroes will also experience reduced mobility on the battlefield with the Plate Mail on.
The artifact is like a double-edged sword, and should be replaced by a better armor as soon as possible.