The door of the Hollow opened, the welcoming creak inviting the
Potters to see who had come to visit. 

James' eyes widened as he saw who had arrived.

"Peter?"

"I'm sorry, James", he replied, answering the implicit question by
stepping away from the door.

"Bellatrix!"

Lily didn't wait to hear another word, but was already running into
the kitchen where Harry lay.  Behind she could hear screams, and the
footfalls of a pursuer.  

She almost threw the crib into the fireplace and grabbed at the flue
powder.  Seeing Rabastan entering, she tossed the powder over the baby
and shouted "Sirius!".