TenSoon is of the same generation as OreSeur, the kandra whose contract was purchased by Kelsier and passed to Vin. Under orders from Zane, who had TenSoon's contract from Straff Venture, the kandra tortured, killed, digested, and replaced OreSeur. He was the first kandra to ever kill and replace another kandra. He possesses the Blessing of Potency, stolen from OreSeur's corpse, as well as his own Blessing of Presence. Because of this, he is believed to be one of the strongest kandra ever.
TenSoon is notable for his possession of a set of bones from a large wolfhound. This gives him the ability to keep up with Vin during her activities as a Mistborn. During this time, he spies for Zane, but also comes to respect and like Vin. When Zane orders him to help kill Vin, he gives Vin the hint she needs to figure out how to control kandra. Though the contract requires absolute loyalty to the contract holder on every issue not specifically relating to the kandras' secrets, TenSoon wanted Vin to use the knowledge to defeat Zane. Vin does so, and uses TenSoon to help kill Zane. In the process, TenSoon is seriously injured, but is able to use his two sets of wolfhound bones to assemble a new skeleton.
After the death of Zane, TenSoon returns to the Kandra homeland. There, he confesses to having aided another against his rightful contract holder and to having revealed the kandras' secret weakness. He is imprisoned by the Second Generation in a deep stone pit, without a skeleton and with very little food and water.
After a year of imprisonment, the Second Generation decides to execute TenSoon. By kandra law, TenSoon must be given a chance to speak first. He is given a skull, but they attempt to kill him with acid before he can form the necessary parts to speak. He cries out for judgement, and insists on it even when the kandra with acid try to convince him otherwise.
TenSoon's judgement is attended by many kandra and presided over by KanPaar. The First Generation do not grant him clemency, so KanPaar announces that sentencing will take place in one month.
During that month, TenSoon is imprisoned in a cage in one of the main caverns of the kandra Homeland. His treatment by other kandra varies, depending on the generation. Fourth and Fifth Generation kandra spit on the ground in front of his cage, to show solidarity with and devotion to the Second Generation. The Sixth and Seventh Generation mostly show pity, while the Eighth and Ninth Generation are mostly curious, surprised that a kandra of an early generation could fall into such disgrace.
MeLaan, a kandra of the Seventh Generation who was raised by TenSoon, comes to visit him in his cage. She believes his claims that Ruin has returned, and reports to him about the return of the mists during the day and the heavy, constant ashfall. She believes they are signs that he is correct, and asks him to lead a rebellion against the First and Second Generation. However, he refuses to fight other kandra. When she asks him about the wolfhound body he was wearing when he arrived, he lies to her and claims to have hated the body, knowing the Fifth Generation must be listening.
For the sentencing, the Seconds send the wolfhound bones to TenSoon, intending to shame him. When KanPaar announces his sentence – ChanGaar – TenSoon uses the speed of the wolfhound body to escape. Instead of heading straight for the entrance, as would be expected, he charges KanPaar. KanPaar's crystal True Body breaks, and TenSoon is able to escape in the confusion, leaping over the crowds clogging the tunnels.
- TenSoon is first encountered in Mistborn: The Final Empire. When Elend Venture returns from one of the balls, he sees his father, Straff Venture, in his office, speaking to TenSoon. At the time, TenSoon is wearing the body of a servant from House Hasting.