It seems you’re asking for the full story of Outlander Season 2, Episode 13, titled (often abbreviated as “DDC” by some fans, though the standard code is “S02E13”).
Claire meets with (Richard Rankin), the grown son of Reverend Wakefield. She asks Roger to help her find evidence of what happened to the Jacobite soldiers after the Battle of Culloden.
Claire explains why she left: on the eve of Culloden, she was pregnant with Brianna. Jamie, knowing the battle was a suicide mission, forced her to go back through the stones to the 20th century to save their child.
But has been doing more research. He found something Claire didn’t know.