Under Lock and Key - S1.E5

Mark's story is fully revealed. When he lived in Belfast, he had a girlfriend, Siobhan Doyle. She was supposed to follow him but never did. Siobhan died soon after. His father told him she had died of TB. Instead, she had died at childbirth without him ever knowing. Mark realises how much Siobhan suffered, and is heartbroken. She was sent to a convent. To his utter shock, he finds out that the child survived: a baby girl. He tries to find her, but the nuns will not tell him anything. An accident occurs that forces him back to work: RMS Olympic, a ship in the same class as Titanic, has had a serious accident. Mark is asked to study the implications. Mark's new discoveries are now less important that delivering on schedule. Pirrie and Andrews discover that Mark Muir is a Catholic, but guard his secret.