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Mona's gun skidded across the gravel and stopped beside Sasha's feet; Mona and Spencer continued to wrestle on the edge of the cliff and were too busy (Mona with trying to push Spencer off the cliff and Spencer with trying to stop herself from being pushed off of the cliff) to notice Sasha pick up the gun in her quivering hand.
Sasha and Spencer had discovered A's identity and were then kidnapped by Mona, who turned out to be A, a backstabber, and a fantastic liar. She'd fooled them all into believing she was Hanna's friend and would always be there for Hanna (and Emily, Aria, Spencer, and Sasha… to an extent. Everyone knew Hanna would always come first in Mona's book), even Spencer, the smartest girl Sasha knew. That's why it came as such a surprise when Spencer and Sasha discovered Mona to be A.
Mona was targeting Sasha more so than Spencer on that night (probably because Sasha was Alison's sister, and every time Mona looked at Sasha, she was reminded of the girl that did nothing but torture her); she loved messing with Emily, Aria, Hanna, and Spencer's lives, but she wasn't determined to take their lives, like she was with Sasha. She would have killed Sasha if Spencer hadn't gotten in the way and tackled Mona. Now they were wrestling on the edge of a cliff.
Mona was pushing Spencer back, and Sasha stared at Spencer's feet, which were slipping and sliding in the thousands of tiny pebbles littering the ground on the very edge of the cliff. Spencer was white with fear, and if Sasha didn't know any better, judging by Spencer's skin tone, she appeared to be dead already. Sasha knew she was still alive, but she was coming closer and closer to tumbling down the side of the cliff. She was still alive, but she wouldn't stay that way if Sasha didn't do something.
Mona's back was facing towards Sasha; she was pushing Spencer so close to the cliff, Spencer had to bend her back to maintain her balance, effectively out of the way with her torso bent back until she was level with Mona's chest. This meant Sasha could get a clear head shot without worrying about Spencer getting hurt.
Sasha raised the gun; Emily and Alison had once taught her how to shoot one, and she remembered Alison telling her to never use a gun unless it was absolutely necessary and only in self defense or to protect another person.
Sasha's trembling finger rested on the trigger. If she could just press down, there would be a hole in Mona's head, and she'd never hurt anyone ever again…
She couldn't do it.
Sasha lowered the gun and fired a bullet into Mona's leg, jumping at the loud crack the gun made as it spit the metal piece out of it.
Mona yelled and fell to the ground, clutching her rapidly bleeding leg, and Sasha watched as the scarlet liquid covered Mona's hand.
Sasha remembered all the times Mona had caused Spencer, Aria, Hanna, and Emily to bleed, to cry, to tremble in their beds, afraid to fall asleep. She remembered pain. Pain after Alison died. Pain after Hanna got hit by Mona's car. Pain after Emily was sent to the hospital with an ulcer, caused by all the stress she was under (most of the stress was caused by A) Pain after Aria was put in the middle of her parents' fighting after A told Aria's mom about Byron's affair.
Sasha felt a burning anger in her gut, stronger than anything she'd ever felt before, and the rage was so intense, everything went black for several terrifying moments.
When Sasha came back to herself, her hands were around Mona's throat, and the already injured girl was rapidly turning blue. Spencer was dragging her off of Mona with all the strength she had left in her weakened and bruised body.
"I-I-" Sasha couldn't continue, but luckily, Spencer understood. Spencer always understood her, meaning Sasha was closer to Spencer than the other three (although she loved all four of her friends more than she loved herself).
"I know," Spencer assured her, enveloping Sasha in a hug. They had almost forgotten about the bleeding and unconscious, but still breathing, Mona lying on the ground at their feet. "It's over… and don't worry, this can stay between us," she murmured as police cars, along with Hanna's car, appeared on the scene.
"I love you, Spence," Sasha managed.
"I love you, too, Sasha," Spencer whispered into her ear.