Hi, I'm reading "It"by S. King; two boys are looking at a photo album;
"There is no school picture of George in here". Richie said. He looked at Bill with a mixture of relief and exasperation. "What kind of line are you handing me, Big Bill?"
"This picture (..) is the last one in the book. (..)"
I'don't understand the meaning of the question: What kind of line are you handing me?
To speak according to the official "company line" or "party line" (politics) is to say what you are supposed to say about a situation.
A "line" may also be used in sales, to tout the benefits of what you are selling.
This may or may not be the whole truth.
So questioning what kind of line one is being given is to question the truth of a statement.
Yes, but this is among friends, it seems, so the tone is light-hearted.