The Second Merchant is on the verge of a journey to Persia, and therefore needs every penny he can get.
He has lent a substantial amount of money to Angelo which he now wishes to have repaid. He has not been a pressing creditor, but when money is required he is quick to hire out an officer to arrest Angelo if the latter should default. As he needs to leave quickly, he has no inclination to listen to a sparring match between Angelo and Antipholus of Ephesus and has Angelo arrested. He is shocked to hear Antipholus of Syracuse deny events that he has witnessed, and challenges him to fight, though he regrets this when he realizes that the man is mad. He testifies before the Duke to all he knows.