I'm scratching around looking at Lucretia Garfield. Her husband was born in a log cabin and assassinated. Their first child was nicknamed Trot from David Copperfield. I'm guessing the friend was Henry Beecher Stowe (just to be different) ... Google search does provide a slight link with Copperfield but apart from that I cannot for the life of me get a connection to Uncle Tom's Cabin. And as for 'keys' ...