"I'm sorry, ma'am." She's even mostly sincere. "However, I now need to make sure everyone else is safe."

"How are you supposed to make sure anyone is safe when you couldn't even protect him!?"

"We're sending a message to our Sect that something went wrong, and we'll keep a better eye on everyone, now. It'll be easier if people follow our directions, though - like not messing with the flags - since we know what's dangerous and what isn't." What has the world come to that she's advocating obeying rules...

"If you could do that, you should have done it sooner! Your useless sect! You send nothing but children, and now my son is dead!" 

"Leave her alone. Your son was instructed to stay out of the West Courtyard, and instead he snuck in and stole an incredibly dangerous magic artifact! That's his own fault, not mine, not hers. You can't just treat these people who came out all this way to help you as though they were your servants!" 

"How dare you speak to me like that! My shameful sister's insane bastard, you're lucky we house and feed you! Get him out of here!" she orders her husband, shoving on his shoulder. 

Her husband, seemingly dazed by the loss of his only son, just shoves back. She goes sprawling, looking at him with more bafflement than anger. He's never even defied her before, let alone shoved her around. 

...Okay something's really off.

"Ma'am, calm down - sir, step back - "

Madam Mo does not calm down, ordering one of the servants to get her husband out of here. Her husband doesn't react to anything anyone says. 

Could be grief, but... All this commotion definitely isn't helping, anyways.

"Stand back!" she orders the servant, voice loud and sharp. "Madam Mo, you as well." She positions herself in front of the man, examining him, hand not quite on her sword but near enough to it.

"Sir," she says, firmly. "I need you to step back."

He does not respond. 

Okay. Usually even people in shock respond - at least flinch, even belatedly.

Not taking her eyes off him, she orders two of the other junior disciples to get the other members of the household away, and check everyone else for unresponsiveness, and then another two to come assist her. (If he's in shock, she should get him somewhere calm and protected. If something worse is wrong, she should get him under guard and separated from anyone without the ability to defend themselves.)

Nobody else is unresponsive. 

After a few minutes he collapses, as desiccated as his son. 

She steps back, slightly surprised, then masters herself.

...Does he seem to be missing an arm like his son was, too?

Sort of hard to tell, he collapsed on his left side. 

Okay. The other disciples need to check people again for unresponsiveness. (She pokes him with her sheathed sword to turn him over.)

Before her sword touches the body, all the lights in the room go out. 

Okay! Bad! 

She lights a flame talisman.

The body is lying slightly differently and the arm is gone. 

Okay this thing doesn't like being looked at, or doesn't like the light - everyone needs to get out in the daylight now. Orderly.

Is anyone new not responding?

Madam Mo. And her left hand does NOT match her right; it's a man's hand, gnarled and burly. 

If she gets in trouble for this so be it.

Lan Fengli is very fast, something she uses to lunge for Madam Mo, sword lashing for her left arm.

The arm twists out of the way in a way no living human arm could and lunges for her throat. 

She twists out of range, trying to position herself so any lunges on the arm's part will make it vulnerable to being run through.

The arm goes for one of the servants instead. He goes down gurgling. 

It takes more than a second to strangle someone.

She starts singing to try to pacify the arm. And also keeps trying to pin it with her sword without exposing herself or anyone else, focusing most on keeping it from killing anyone else.

It slows, a little. 

The servant's neck goes crack. 

Slows a little hopefully means stabbable!