What did Mrs. Douglas reveal about her husband’s life in America and Bodymaster McGinty?

From the text:

Mrs. Douglas thought earnestly before she answered. “Yes.” she said at last, “I have always felt that there was a danger hanging over him. He refused to discuss it with me. It was not from want of confidence in me—there was the most complete love and confidence between us—but it was out of his desire to keep all alarm away from me. He thought I should brood over it if I knew all, and so he was silent.”
“How did you know it, then?”
Mrs. Douglas’s face lit with a quick smile. “Can a husband ever carry about a secret all his life and a woman who loves him have no suspicion of it? I knew it by his refusal to talk about some episodes in his American life. I knew it by certain precautions he took. I knew it by certain words he let fall. I knew it by the way he looked at unexpected strangers. I was perfectly certain that he had some powerful enemies, that he believed they were on his track, and that he was always on his guard against them. I was so sure of it that for years I have been terrified if ever he came home later than was expected.