Imagine a 19th century mystery that begins with a man slipping in and out of consciousness in a Baltimore hospital bed in clothes that are not his own. While he has periods of semi-lucidity, he is more often wracked by delirium, incoherently babbling and shouting out the name "Reynolds" to the puzzlement of all around him. After a short period of recovery, he suddenly takes a turn for the worse, says "Lord, help my poor soul!" and dies.
This is the 19th century, so the cause of death is listed as alcoholism, because how else can you explain such strange symptoms. But in reality, no one knows. Nor do they know how the man came to be found unconscious in a city he wasn't supposed to be in wearing someone else's clothes after having disappeared for five days.