"Working on Borrowed Time" by John G. Hemry

An interesting time travel story whose title has a double meaning made clear in the story. A time traveller travels back to London, 1908 to try to prevent a disaster that should not happen from happening, creating an alternative future. He encounters a master assasin who is there to make sure the alternative future does happen, and help in the form of another traveller who is also there to prevent the disaster.

• Read from Analog SF, June 2005