Katherine Valentine is the daughter of Thaddeus Valentine, Head of the Guild of Historians and a popular Londoner.
Katherine grew increasingly estranged from her father, especially after learning from the Apprentice Engineer Bevis Pod that Valentine pushed Tom down the chute. Together, the two learned that Valentine's energy project in the re-purposed St Paul's Cathedral is more than it seems.
Katherine helped Tom to destroy London's engine core to slow it down, preventing it from crashing. The surviving Londoners, led by Katherine, make peace with the Anti-Tractionists. But the Ancients destroyed much of Earth, killing Katherine in the process.