Border Princes is a novel based on the British science fiction TV series Torchwood, written by Dan Abnett. Like the TV show, the novel is set in Cardiff and features a team of elite agents from the Torchwood Institute who deal with extraterrestrial and supernatural threats to humanity. The story begins with Captain Jack Harkness, the leader of Torchwood, getting a strange message on his Vortex manipulator, a time-traveling device. The message is from one of Jack's old acquaintances, an intergalactic arms dealer named Bilis Manger, who Jack thought was dead.

Jack's curiosity leads him to investigate the message, and his team also gets involved when they discover that Bilis has a connection to a series of bizarre incidents that have been reported in Cardiff. In one of these incidents, a man is pursued by a strange winged creature and then gets abducted by a group of masked people who seem to be conducting some kind of paranormal experiment on him. Meanwhile, a group of travelers, who call themselves the Border Princes, arrive in town and set up a carnival which seems to be more than just an entertainment event.

As the Torchwood team investigates further, they discover that the Border Princes are actually a group of interdimensional travelers who use the carnival as a cover for their smuggling activities. They also find out that Bilis is working with the Border Princes to obtain a powerful artifact known as the legacy, which has the ability to grant wishes.

The story takes a darker turn when the Torchwood team finds out that Bilis and the Border Princes are not the only ones interested in the legacy. There is another group, called the Darksmiths, who are also after the legacy and will stop at nothing to get it. The Darksmiths are a group of transdimensional beings who feed on the emotions of humans, and they see the legacy as a powerful source of energy for their hunger.

The novel builds up to a climactic showdown between Torchwood, the Border Princes, and the Darksmiths, with the legacy at stake. The Torchwood team realizes that the only way to stop the Darksmiths is to destroy the legacy, even though that means denying Bilis his wish, which they had promised to grant in exchange for his help.

In the final battle, the Torchwood team is able to overpower the Darksmiths and destroy the legacy, but not before some of the team members are injured or killed. The Border Princes, who had initially been hostile towards Torchwood, realize the danger of their actions and decide to help Torchwood against the Darksmiths. Bilis, on the other hand, reveals his true intentions and disappears with the legacy, leaving Torchwood to deal with the consequences of their actions.

The novel explores a number of themes that are common in the Torchwood universe, such as the ethics of using advanced technology to manipulate reality, the consequences of dealing with extraterrestrial and paranormal entities, and the personal relationships among the Torchwood team members. The writing style is fast-paced and action-packed, with vivid descriptions of the bizarre creatures, locations, and events that make up the story.

Overall, Border Princes is a thrilling and engaging novel that will appeal to fans of Torchwood and science fiction in general. It offers a fresh perspective on the Torchwood universe while staying true to the spirit of the TV show, and introduces some new characters and concepts that may have potential for future stories.