Gretchen feigned incomprehension. "Sis, what are you talking about?"

Gwenda's sarcasm was sharp. "Nothing. I just felt God's been unfair, since nothing happened to me last night. So, your plan failed."

Panic flashed across Gretchen's face. "How did you know?"

Gwenda's response was immediate. "You're wondering how I found out, right?"

Gretchen's panic intensified. She pinched her hand, trying to calm herself. Tears welled up. Raising her head, she adopted an innocent, aggrieved expression. "Sis, did I do something wrong?"

"No, how could you possibly do anything wrong? You're always right!" Gwenda's smile was contemptuous. "You pull that face all the time," she thought, adding silently, I used to feel sorry for her, but now I just want to tear her facade apart!

"Sis?" Gretchen's expression remained innocent, despite her confusion.

Martin intervened. "Gwenda, what's wrong with you? Gretchen didn't do anything. Why are you mocking her?"

"Mocking her? That's not the only thing I want to do!" Gwenda slapped Gretchen.

Gretchen, staggered by the blow, covered her cheek. Martin, initially stunned, shouted, "What the hell, Gwenda? I came all the way back for you, and this is how you treat me? Fine, never mind that. But why are you being so mean to Gretchen? Do you know how worried she was last night? She stayed up crying!"

"Oh?" Gwenda raised an eyebrow. "Weren't you on a business trip? How do you know she was crying all night?"

"I" Martin stammered.

Gwenda's smile became more sardonic. "Let me guess. Did she call you and tell you I had an accident? Then cried, and you comforted her?"

Martin was dumbfounded. Gwenda seemed to have witnessed everything.

"So, I got it right?" Gwenda's eyes turned cold.

Gretchen tried to explain, "Sis, it's not what you think"

"Then what is it?" Gwenda cut her off. "Are you saying you're both innocent? That you have no feelings for him? That you've never been interested in him?" Her sharp tone was devastating.

Gretchen was speechless and pale; Martin was embarrassed and unsure how to react. Gwenda's face was frigid. With a look of scorn, she announced, "I'm cancelling the engagement."

"Cancelling the engagement?" Martin's eyes widened.

Gretchen was equally surprised. She realized Gwenda was a changed person. She'd never have considered giving up Martin before.

"Yes! I'll fulfill your wishes. You don't have to act anymore." Gwenda's eyes were frosty. "Get out!"

The final "☐☐☐☐☐☐☐☐☐☐☐☐☐☐☐☐" and "K<--" are unnecessary and have been removed. The passage is now grammatically correct and punctuated appropriately.