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A wrench was a tool. In 2119, aboard the underwater mining base the Drum, a wrench was kept in a room entered by Tim Lunn trying to escape the ghost form of Richard Pritchard. The ghost picked up the wrench, preparing to finish Lunn off, but when it saw that Lunn did not see the mysterious writing on the wall of Albar Prentis's funeral spaceship, it dropped the wrench and walked out of the room. (TV: Under the Lake)