There really are a lot of unknowns in this story, aren't there? Including the character of Lethe (river of forgetfulness, if I'm not mistaken), and that weird toast of Dr. Adams', during which we see Lethe. I'm not sure what was implied here...
"May we never find space so vast, planets so cold, heart and mind so empty that, that we cannot fill them with love and warmth."
Which if nothing else brings up an always-interesting aspect of actors, at least for me. This actress, for all we know, might be the most entertaining, nicest, laugh-a-minute person in the world...but in the episode...my God, look at that (non)expression!