Elena wakes up and finds herself kidnapped by Kai in The Vampire Diaries Season 6 Episode 11. 

They are at the Mystic Grill and Kai explains that he took her to use as his guinea pig for testing all of the magic he absorbed when he channeled the traveler spell. It's been 18 years since he was able to interact with anyone, he often reminds everyone. Their torture moves over to the local high school and Kai succeeds and melting off Elena's daylight ring.

When Elena is able to break free for a free minute, she calls Damon and lets him know where she is and that she needs help. 

Over at the Salvatore mansion, Liv is teaching Jo how to use her regained magic. It's not going very well which is why Alaric went shopping for mimosas.

Damon heads to the high school with Liv, but Luke takes her before she can help. He comes back with Jo and they are able to rescue Elena but she isn't strong enough to keep them all cloaked from Kai. Jeremy and Alaric finally save the day.

Stefan goes with Caroline on a trip to Duke. She wants to talk to the top oncologist and he wants to check on Sarah Salvatore. After an initially successful experiment, Caroline is able to convince Liz to drink her blood. Unfortunately Caroline doesn't know that the side effects take a turn for the worst.