|“|| Derek: "Are you gonna torture me, or are you just gonna talk me to death?"|
Kate: "Oh, sweetie, I don't- I don't wanna torture you. I just... wanna catch up. Remember all the fun we had together?"
Derek: "Like the time you burned my family alive?"
Kate: "No, I was thinking more about the hot, crazy sex we had. But the fire thing? Yeah, that was fun, too. I love how much you hate me. Remember how this felt?"
Derek met Kate when he was around sixteen years old, a short time after he was forced to mercy-kill his high school sweetheart Paige Krasikeva after she rejected an Alpha's Bite, while he was still in high school. Kate, hiding the fact that she was a member of the Argent Family and a Werewolf Huntress, seduced Derek, taking advantage of his youth and grief in order to gain more information about the Hale Family under the guise of engaging in a romantic and sexual relationship with the young man.
In late 2004 or early 2005, Kate and a number of cohorts set the Hale House on fire, killing Talia Hale and the rest of the Hale Family (including both Werewolves and Humans alike) with a few exceptions: Derek and his older sister Laura, who were at school; Cora Hale, who, believing her whole family to be dead, escaped the house and went on the run; and Peter Hale, who was so badly burned that his body became comatose to help speed up the healing process. Derek and Laura ultimately fled Beacon Hills and went to New York, where they would stay for the next six years without any news or contact with Kate or the other Argents.
In 2011, Derek returned to Beacon Hills shortly after Laura was lured back by news of a spiral burned into the corpse of a deer, where he found his sister cut in half in the woods. It wasn't long before the Argent Family, who had also recently relocated to Beacon Hills, found out that Derek was there, and, unbeknownst to Kate's brother Chris Argent, Kate and a pair of fellow Hunters came to the Hale House ruins in an attempt to get information about the new Alpha in town. During this interrogation, Kate revealed that, while the Argents weren't responsible for Laura's death, they were responsible for cutting her body in half so she couldn't heal as per their tradition.
Kate continued to manipulate and taunt Derek while attempting to convince Chris and his wife Victoria Argent to go harder in killing Derek after learning that the Alpha was Peter Hale, who had recently recovered from his coma and immense burns after killing Laura and taking her powers. However, in the final battle, Kate was killed by Peter, who clawed her throat out in front of Derek, Chris, the new Beta Werewolf Scott McCall, the young Huntress Allison Argent, and their two human friends Stiles Stilinski and Jackson Whittemore.
However, unbeknownst to anyone at the time, Kate was scratched so deeply by Peter's claws that, though she was dead for a time, her body ultimately resurrected itself as she transformed into a Werejaguar right before the full moon. When she was unable to control her transformations, she got the idea to capture Derek and perform a Age Regression ritual in order to revert him back to when he was a teenager and still trusted her so she could once again manipulate him into helping her; in this case, it was to obtain the Triskelion Medallion, which she believed was a supernatural talisman possessing the power to help her control her shifts. Whether intentional or accidental, this ritual also caused Derek to temporarily lose his Werewolf powers after he was returned to his adult self, though he ultimately learned it was actually an evolution into a Werewolf with advanced shapeshifting abilities. Once Derek had finished evolving, Derek, in full-wolf form, attacked Kate, weakening her considerably.
The two did not see each other for over a year, as Kate had gone on the run from the Calavera Family of Hunters, her own brother Chris Argent, and her former co-conspirator to kill Scott, Peter Hale, while Derek left Beacon Hills to travel South America. They ultimately reunited in Season 6's Broken Glass, when Kate tracked Derek and Chris to the site of a Hale Vault in North Carolina and stole a large vial of yellow wolfsbane from Derek. Though Derek argued that Gerard would never fully trust her due to Kate being a supernatural creature like those he hunted, Kate retorted that her intent was only to make a bullet with which to kill Scott, causing Derek to decide to return to his hometown to save him from her.
Throughout Teen Wolf
In Magic Bullet, though Derek and Kate do not physically interact through conversation, they are shown to be in the same vicinity upon Kate's arrival to Beacon Hills; Kate was being pursued by the Alpha Werewolf whose identity had not yet been revealed, and Derek was pursuing the Alpha, as he was curious as to who it was and suspected that it may have stolen his sister Laura Hale's Alpha powers.
After the Alpha attacked Kate in her SUV at a four-way stop, Derek, continuing to chase the Werewolf, was caught in the crossfire and was shot by Kate with a sniper rifle; the round was packed with Nordic Blue Monkshood, a rare and lethal form of Wolfsbane that could kill a Werewolf in a matter of days. When Kate's brother Chris Argent arrived as back-up, the two discussed the fact that Kate had shot a Beta, though neither of them were certain that it was Derek, and Kate informed him that the wolf she shot would likely only live another forty-eight hours or so, potentially hampering their ability to use them to find the Alpha.
Derek, knowing that he had been shot by Kate, sent the newly-turned Beta Scott McCall, who was dating Kate's niece Allison Argent, to steal a bullet from Kate's property in order to save his life. By the end of the episode, Kate was certain that it was, in fact, Derek whom she shot and assumed that whomever the Alpha was, he was connected to him somehow. She also believed there was a second, smaller Beta involved with them as well, but had no idea who it could possibly be, protecting Scott's cover as an ordinary human teenage boy for a short while longer.
In The Tell,
In Heart Monitor,
In Wolf's Bane,
In Code Breaker,
In The Dark Moon,
In The Benefactor,
In Time of Death,
In Broken Glass, Chris Argent, Kate's older brother and a friend and ally of Derek, tracked the latter down in North Carolina in hopes of gaining his help in the McCall Pack's battle against both the Anuk-ite and the army of Hunters led by Gerard Argent and Tamora Monroe. Though Derek was initially resistant, he eventually agreed to help out of loyalty to Scott McCall, but only after he took care of an issue first.
Argent was shocked to find that Derek's errand included hiding a large vial of liquified yellow wolfsbane, which he revealed was the reason behind Gerard and Monroe's Hunters killing the Werewolf pack in Brazil. Argent begged Derek to get rid of it, but Derek refused; this was partially due to the fact that it was both a poison and an antidote as well as the fact that he knew Gerard wanted it. Before he could hide it in the second known Hale Vault, a handful of FBI agents appeared with their guns aimed at Derek, who had been blamed for the murders of the Brazilian pack's members.
Suddenly, a female agent appeared behind them and shot all of the agents in front of her before shooting at Derek and Argent as well, though they were intentionally non-fatal shots. Since Derek had inadvertently dropped the vial after being shot in the side, it was very easy for Kate to steal it from him as she greeted him with "Hey, handsome," just as she did when he was a teen. After some bantering between the two (which, on Kate's end, also involved some physical violence), Derek asked Kate if she was really that desperate to get back in her father Gerard's good graces and reminded her that she was what he hunted. Argent, too, agreed with Derek and pointed out that Gerard had too much hate to have any love left over for her.
Unfortunately for them, she wasn't as concerned with winning Gerard over as she was with vengeance, and she informed them that she intended to put the wolfsbane in a bullet with which to kill Scott McCall before she ran off. Derek, still healing from the gunshot, got up and limped after Kate, advising Argent to leave to go warn Scott while he pursued the Werejaguar.
In The Wolves of War, Derek, knowing that Kate would be going after his friend and ally Scott McCall in an attempt to kill him with a yellow wolfsbane bullet, returned to Beacon Hills for the first time since Season 4's Smoke and Mirrors in order to help defend Scott against her.
- Derek and Kate's relationship is often compared to the relationship between Scott McCall and Allison Argent as part of the show's ongoing theme about history repeating itself.
- Both relationships involved a young Werewolf (Derek and Scott) getting into a relationship with an Argent Hunter (Kate and Allison, respectively), though Derek was unaware that Kate was a Hunter while Scott had known that Allison's family hunted Werewolves since just a few short days after he was bitten and turned.
- Both Allison and Kate spurned the original Hunter's Code, "We hunt those who hunt us", with Kate completely ignoring it by killing Werewolves and other supernatural creatures indiscriminately, and Allison choosing to make a new, more benevolent Code, "We protect those who cannot protect themselves," a Code that included protecting benevolent and vulnerable supernatural creatures as well as their human counterparts.
- Derek and Kate's relationship was the first romantic relationship to be shown for either character in the series.
- In Kate's case, Derek was the only romantic/sexual partner she was seen to have, though it has been implied that Kate was a very sexual person who liked to have flings, while Derek was shown to have been in a relationship with Paige Krasikeva prior to meeting Kate, and in a relationship with both Jennifer Blake and Braeden afterward.