See: Conquest and Krakkan.
The Kestrel Key of Krakkan was created because of a wager that took place one thousand years ago by the Octessence, eight mighty beings. They each put their power into an item and decided that the first mortal to come into physical contact with each being's respective item would become an Exemplar, possessing the power of the being who created the item they interacted with.
One Exemplar was Bridget Malone, the one who activated the Kestrel Key's power. She worked with the other Exemplars to fight against Juggernaut who had betrayed the will of the Octessence. But thanks to Captain America, who used Bedlam, Krakkan's influence was driven out of Bridget but the Key still gave her its power.
Its current whereabouts are unknown.
It gave Bridget the ability of superhuman reflexes and fighting skills as well as a vast array of weaponry all over her costume.