Tom Natsworthy is the main protagonist of the Mortal Engines Quartet. An apprentice Historian at the beginning of the series, he eventually has diverse adventures across the world. He admires the head of historians (Valentine) and has a strong sense of curiosity.
When he was twelve, he won a Guild prize for an essay on identifying fake antiquities.
By the time he was fifteen years old, Tom was a Third Class Apprentice, working under Chudleigh Pomeroy. He observed London's capture of Salthook, but was sent to the Gut after a brawl with Herbert Melliphant.
Tom was accompanied by his hero, Head Historian Thaddeus Valentine, as well as Valentine's daughter Katherine. Together, they approached the Salthook scavengers to purchase Old Tech. However, one was an assassin in disguise, and attempted to stab Valentine. Tom managed to stop the attack, and pursued the girl towards the furnace district.
The would-be killer revealed her name to be Hester Shaw. She claimed that Valentine was responsible for her disfigurement before leaping down a waste chute. Shortly after, Valentine arrived and to Tom's surprise, pushed him down after her.
Together, Tom and Hester trailed London, eventually being picked up by Speedwell. However, the mayor had the pair drugged with the intention of selling them as slaves. They managed to escape, chased by the slavers. They were rescued by Anna Fang, who smuggled them to Airhaven aboard the Jenny Haniver.
Tom, Hester and Anna dined at the Gasbag and Gondola inn, accompanied by several of her Anti-Tractionist friends. The dinner was interrupted by the arrival of Shrike, a Stalker sent by London mayor Magnus Crome to kill Hester. While the aviators held off Shrike, Tom and Hester escaped Airhaven on a hot air balloon.
The pair then climbed onto the pirate suburb of Tunbridge Wheels. Chrysler Peavey took a shine to Tom, considering him a "gentleman" for originating from London. However, the brutality of the pirates caused Tom to grow disillusioned with the concept of Municipal Darwinism. After Peavey's men mutinied, Shrike caught up with Tom and Hester. The Stalker revealed his intention to kill Hester and have her resurrected as his daughter, but before Hester could be executed, Tom stabbed and killed him.
Tom and Hester then reunited with Anna, who took them to Shan Guo to warn the citizens of MEDUSA. Tom spotted Valentine disguised as a monk, and raced to find Anna and Hester. Witnessing Valentine kill Anna, he resolved to return to London with Hester and help her kill the Head Historian.
Hester, meanwhile, was captured and taken to Valentine. However, she was freed after Katherine was stabbed and fell on MEDUSA's console, causing it to malfunction. She quickly left London with Tom in the airship. MEDUSA finally misfired, obliterating most of the city and killing Valentine. Hester tried to comfort a grief stricken Tom as they flew away in the Jenny Haniver, apparently the only survivors of the incident, and made their way to the Bird Roads.