Both Mettus and his older brother Tullis—Phlox's second youngest child—never saw "eye-to-eye" with their father Phlox, and the two had not spoken with Phlox for sometime prior to 2152. (ENT episode: "A Night in Sickbay" and ENT - Rise of the Federation novel: Live by the Code)
Phlox tried to raise Mettus free of prejudice against Antarans. Mettus fell in with unfortunately accepted views of other influences in his life, choosing instead to embrace the prejudices, creating a rift between him and his father. This caused the two to become estranged for ten years.
While Tullis eventually came around and patched things up with his father, Mettus was still estranged from his family in 2165. When his sister Vaneel married the Antaran Pehle Retab, Mettus and some of his fellow extremists crashed the wedding. Mettus tried to force the cancellation of the wedding, however he was firmly rebuffed and left in anger.
Mettus later confronted the wedding party and killed Pehle's father Sohon Retab—a popular Antaran politician. Mettus was taken prisoner by the Denobulans, who were considering extraditing him to Antar to face trial. Mettus was kidnapped by the True Sons of Antar, who intended to execute him after a show trial. Phlox went to Antar and was able rescue his son before the extremists could kill him, taking an energy blast meant for his son.
Afterwards Mettus was taken into custody by the Antarans. After his trial Mettus was imprisoned at Tileb Prison on Antar. When his father came to visit him Mettus admitted that the prison was nothing like what he thought it would be—it was a clean, safe place—and the Antarans treated him fairly well. Given time to think, Mettus began to re-evaluate his choices. When Phlox came to visit him he talked to his father without anger for the first time in years. Phlox forgave him for what he had done, and was confident that Vaneel would be able to do the same in time herself. (ENT - Rise of the Federation novel: Live by the Code)