Davos has decided the time has come to act. He and a small band of followers he has been cultivating kidnap Edric Storm and send him off on one of Salladhor Saan's ships, to protect him against Melisandre's plans to sacrifice him to bring dragons to life.
He tells Davos he thinks Melisandre is correct that Joffrey is dead. Now that three kings have died, that's surely all the proof of her abilities Stannis should need. So he is now ready to sacrifice Edric. Davos tells him what he has done, but points out that it's not treason since he vowed to protect the king's people. Stannis says he'd better have a good explanation, or else he's going to lose his head. Davos starts to read a letter.
I'm betting that once he finished reading this letter either he is going to die or Melisandre is. Because unless this letter has some juicy gossip on her, it doesn't look good for him.
As for the plot to save Edric, can Salladhor Saan be trusted? I don't think so. I think Melisandre gets a lot of her information from him. Though she did seem surprised that Davos had made Edric disappear, it could all have been an act. After all, as Sansa pointed out, in this series it's *all* lies!
