Trevyr Blackgard initially wanted to send Cayman with his son Lucan Blackgard to King's Landing, but Cayman declined, not because he didn't want to be around Lucan, but because he didn't care for King's Landing.
Cayman accompanies Dyron Blackgard in his trip to Rosby to stop Ser Marlen Rosby from abusing Elyse Blackgard any further. When Dyron is attacked by the assassins, Cayman attempts to protect him, but cannot save Dyron from being killed, though he kills one before the other two escape.
Cayman holds himself responsible for Dyron's death, though Trevyr has told him that it was not his fault, Cayman still believes it is.
Ser Cayman gets caught up in the Black Day, attempting to prevent Lord Eddin Blackgard and his wife and children from being killed, but ultimately failing. He is fortunately able to buy time for Lady Sofina Blackgard and Gerrad Storm to escape Ebonheart, but only at the cost of his own life, when his is killed by two fellow members of the Blackgard Sentinels.