James' plan was talk to Lily, warn her, keep Remus' secret safe by doing so, and then finding Remus.
He had drunk the Polyjuice Potion, it's pleasant taste still in his mouth.
"Lily, I have something important to tell you…"
"Why did you tell James?"
"Tell him what?"
"About the potion thing. He ran after me screaming that I was deluded."
"He's mental. What can I say? I think he overheard us."
"Well, great. Now he thinks I'm in love with him."
"Wait, what?"
"Amortentia."
"What about Amortentia?"
"Really? James thinks that I'm in love with him because of the Amortentia he supposedly used."
"Amortentia?"
"Yes! What's with you today? Remember…Severus warned me that he heard James talking with Siruis about me and a potion. He thought it was Amortentia…and then I told you it might be working even though I knew it wasn't there. Do you have memory loss? Or has this got to do with the full moon?"
"I'm sorry. Severus thought I was using Amortentia on you?" said James, confused. Maybe that's why he had the book. He had never thought James was using Polyjuice Potion. He thought James was using Amortentia…and so did Lily! And she said it was working even though she knew it wasn't there…
"Remus, we have to take you to the nurse. You're really confused, and I know what happens on the full moon."
" Nothing is…ugh" he groaned suddenly getting a splitting headache. He looked through the window, and sure enough, the moon was high and shining.
"Let's go!" Lily screeched.
"I- No." said James, talking off to find Remus, Maybe his secret was sort of spoiled now, but they'd just have to trust Lily Evans from then on. And James didn't think the nurse could really do anything against someone turning into a werewolf.