What is Don John's current plan? (Act i, scene iii)

Borachio, another friend of Don John, arrives and informs Don John that he has overheard his brother and Claudio plotting a marriage with Hero. He hid behind a wall hanging and listened to them discuss how Don Pedro would woo Hero and then give her to Claudio. Don John tells them to come with him so that he can figure out a way to thwart Claudio.