We flashback to a younger Elena (we know she's younger because she has a ponytail) and Clay arriving at Stonehaven. They're lovers and he's bringing her to meet "his family" for the first time. So once upon a time they were happy....what went so wrong?
Clay, Elena and Nick follow a lead on the possible wolf killer but come up short on clues. Clay shifts to human form before Elena and pets her wolf form. Elena screams at him "DON'T PET ME!" Nobody puts wolf Elena in a corner!
We get some insight into wolf mythology when we learn that Elena is the word's only female werewolf. Apparently shifting is dangerous for women - something we see by the evidence strain on Elena's face when she shifts twice in this episode.
We flashback to a year earlier. Elena was trying to buy off a guy who was going to expose the presence of werewolves. When he got mouthy and threatened her, Elena lashed out and ripped the dude's heart out! Since then, she's felt major guilt and struggled to hang onto her humanity.