Life Knife

The Life Knife — as coined by Ianto Jones — was a three-bladed knife (8 inches deep by 3 inches wide) of extraterrestrial origin used by Suzie Costello to kill people in order to test the resurrection gauntlet. The knife was associated with the glove as they were made of the same metal, and those killed with the knife were easier for the glove to resurrect. (TV: Everything Changes, They Keep Killing Suzie)

After Suzie's death, the knife was locked away in Jack Harkness's safe sealed with a "NOT FOR USE" tag. Torchwood Three, however, had to retrieve it to make the resurrection gauntlet effective on Suzie herself. Jack stabbed it into her chest, and she awoke from death immediately. The Torchwood team learned that use of the Life Knife in tandem with the gauntlet presented an extreme risk to whoever awoke a subject from death- siphoning of their own life force to fully resurrect. Toshiko Sato shot the glove into pieces, cancelling out its effect, and the Life Knife was once again returned to its proper place in the Hub's secure shelves. (TV: They Keep Killing Suzie)

The Life Knife was presumably destroyed, lost, and/or buried with the destruction of the Hub by a mile-wide radius bomb, which engulfed nearly all of the underground base. (TV: Children of Earth: Day One). Its former owner Suzie, however, came back to life a second time for revenge. (PROSE: Long Time Dead)