A high school boy talking to the phone:
To me it seems (context-wise) that he's covering for his childhood friend (in the story) who didn't come back home yet, saying that he's going to stay the night at his place.
But a translation that has been made for it was like this:
"I'm gonna be out for a while..."
"Looks like I'll be spending the night."
"I'll let her... know!"
In this translation, it seem that he's talking to his parent telling them he's gonna spend the night out.
After the scene, there's nothing that indicates which one is correct.
I hope to get an opinion of someone more knowledgeable than me to see which translation is/seems more probable.