Word Count: 1421
Isaac is not the type to trust easily. The world he knows is full of pain and loneliness and no one has breached into his bubble of space since he was nine years old and someone threw Matt Daehler in the pool.
So yeah, he doesn't...he doesn't trust.
When Derek helps him out of the grave, he's wary of the strength Derek uses to move the bull dozer and then hoist Isaac upward. Derek is nice, though, talking to Isaac amicably, smiling.
Isaac finds himself relaxing, until Derek asks if he wants to be strong, to get out, to be like him.
Derek's face changes then, and Isaac freezes the way he's learned over time. He read in a biology textbook one time that rabbits and mice do that to avoid being seen by hawks and owls, and Isaac kind of feels like a rabbit all the time.
Derek asks again, "Do you want to be like me?"
The yes burns in his throat, but he keeps his mouth shut.
Derek says, "Think about it."
His dad gives him a black eye that night and the next day Isaac walks to the train depot Derek was staying in and let's the yes slip free.
That night he lies in bed and listens to his father's heartbeat. It thumps deep and even. Isaac memorizes the sound. He thinks he could pick the sound out of a crowd of a thousand. His dad has always seemed to sturdy and solid, the heartbeat is just the same.
Isaac hates that he likes that.
It doesn't matter though, because he only gets a day to listen to his father's heart. It stops.
Derek teaches him about listening for lies while he's hiding out with him after breaking out of prison.
"The heartbeat changes when they tell a lie," Derek says. "I'll give you a list. Tell me which one is the lie."
Isaac nods. He still hasn't spoken to Derek much because he's not sure he can give him that much.
"The Camaro was my sister's car before it was mine. I bought my first leather jacket when I was 14. I went to college for mechanical engineering. I was born a werewolf."
None of that is anything that matters but Isaac can understand that. Derek doesn't trust him yet, either. That's okay. He thinks about the way Derek's heart sounded in those sentences, and at last, says, "You didn't go to college for mechanical engineering."
Derek looks pleased. "That's right."
They spar after that, and the pain is good because it's fleeting, even if it's still terrifying to be able to hit back and to hear the sound of bones crunching.
But he finds it's easier if he focuses on the rhythm of Derek's heart. It's racing with exertion right now, but his is too, when he listens to it. They almost match in rhythm.
"This is for your own good," Derek says while Isaac is sprawled on the ground, still healing a broken leg.
Derek's heart rate doesn't change, and Isaac thinks if he had been able to hear his father's heart after receiving a black eye ("You deserve this.") there wouldn't have been a skip in that rhythm, either.
He knows what to expect from Derek, then, so he guesses he trusts him.
Erica is easier to trust because she immediately trusts Isaac. He never asks, but she tells him anyway, like she can hear him wondering. "You never laughed," she says, and it's true; he didn't.
So when he and Erica are sent to the school to capture Lydia, he lets himself laugh and relax around her.
Well, not relax. He fronts with as much cocky swagger and anger and psychotic bloodlust as he can. He feels most comfortable this way, when everyone else is scared of him. Faking it is safe. He's untouchable.
Erica gets mad when Lydia is gone; Isaac can hear her heart starting to race. Neither of them want to disappoint Derek.
So he channels Erica's anger and turns it into his own. He grabs Matt by the neck and snarls at him. He barely pays attention to Danny looking freaked out. He doesn't care.
Erica's heartbeat doesn't slow down as they tear off in the direction Stiles and Allison took Lydia.
There's a moment, after he calls Derek, when they're both so scared that Derek is going to break their arms again, and Erica's heart is racing in time with his, where he reaches out and takes her hand in his. They don't stop running until they reach Scott's house and stand on the street, scared and waiting for Derek.
Boyd is a lot like Derek, minus the crippling depression Derek doesn't admit to having.
Isaac doesn't know if he trusts Boyd, because Boyd always looks like nothing is bothering him, even though his heart races when Derek levels a glare at him, or when Derek tells them he has to chain them up for the full moon and leave himself defenseless, or when Derek gets shot by the hunters.
Boyd's face doesn't change, but his heart does. And Isaac can trust a heartbeat.
Slowly he figures out who Boyd is, that he's never really been the type to show emotion. Isaac can understand that, because sometimes showing emotion is like showing weakness.
But then Boyd leaves, and he takes Erica, and Isaac loses two sets of heartbeats.
Scott's heartbeat is all full of lunges and hiccups. He's never met someone who's so all over the place, and he knows Stiles. But Scott is constantly panicking about werewolves or hunters or his girlfriend or Gerard or his mom.
It's hard to know if Scott is lying.
But his heartbeat still tells the truth. Scott worries about everyone (Allison is at the top of the list, but everyone else falls pretty close to the top) all the time and he wants to make the world better. He wants to make people better.
He's the nicest person Isaac has ever met, so when Boyd and Erica ask Isaac if he wants to come, he asks Scott for advice.
He doesn't say, "Derek is still important to me." He says, "I don't have anyone."
Scott doesn't call him on the hitch in his heartbeat, he just says, "I'll be here."
So when Boyd and Erica leave, Isaac leaves too, only he runs to the Beacon Hills lacrosse field and throws himself onto the bench next to Scott.
Scott's heartbeat stutters in surprise and he gives him that lazy, crooked smile and—
Okay, Isaac trusts him. Of course he does.
Stiles lies more than Boyd and Derek put together. Everything he does is a lie. Because he always says he's fine, whether he's speaking the words or acting the part.
Isaac likes listening to Stiles' heartbeat, because as more time passes, the beat evens out. But then he hates it because it means that Stiles is starting to believe that he is fine.
The moment where Jackson and Lydia embrace, because Lydia still loves Jackson, there's a moment of truth in Stiles.
His heart speeds up and he cries silently but doesn't say a word. He doesn't see Isaac watching and listening, wondering what happened to his face—
But then Stiles is crossing the warehouse muttering about his Jeep and brushing Scott off.
Stiles is lying again, but his heartbeat doesn't tell Isaac that.
I'm fine. I'm fine.
The lub-dub sound is steady. But Stiles isn't find and Isaac thinks he gets that.
He doesn't have time to mention it, though, because Derek is grabbing Isaac's arm and pulling him up, hand brushing over his back, where Allison stabbed him.
"Are you okay?" Derek mumbles, and he sounds so scared, like he cares about Isaac's welfare.
He does, Isaac reminds himself. "I'm fine," he says, practicing. He listens to his heartbeat. It skips.
But he has time.
"I'm fine," he repeats, and he glances back over his shoulder at Stiles climbing into his Jeep and backing out of the warehouse. "I'm fine."
Derek justs clasps his shoulder. He looks gutted by Scott's dismissal, and Isaac knows he can never leave Derek. He doesn't know how Erica and Boyd managed it.
He swallows. "Can we...Can we leave?"
Derek nods and the pair of them walk through the hole in the wall made by Stiles' Jeep.
"I'm fine," Isaac whispers again, and his heartbeat barely changes.
Derek squeezes his shoulder. "It's okay."
His heartbeat is steady.
Disclaimer: I don't own Teen Wolf.
A/N: I don't know why this isn't romantic, or why I have to name all stories about Isaac after songs but apparently that is A Thing I Do. So.