The basics (from tvguide.com):
Synopsis: Mick's past comes into sharper focus for Beth when the grandson of his World War II buddy is kidnapped. The disappearance forces Mick to deal with some secrets from his troubled life.
Written by: Jill Blotevogel
Directed by: Chris Fisher
Original Air Date: May 9, 2008
Guest Cast:
Eric Winter: Benjamin Talbot
Daniel Goldman: Jacob Fordham
Robin Thomas: Robert Fordham
Bonnie Burroughs: Julie Fordham
Justice Leak: Ray Fordham
Mercedes Connor: Lilah Fordham
Todd Giebenhain: Leo
Anthony Starke: Ken Verdolino
Erika Ringor: Det. Theresa Novak
My own thoughts about this episode:
This is one of my favorite episodes of Moonlight in some ways, because it gives us amazing insight into Mick long before he became a vampire, and also does a great job of circling back to give us new ways of looking at elements of his past, Beth's past, and even Josef's past. Not surprisingly, it was written by one of the great Moonlight writers, Jill Blotevogel.
Running through this episode like a ribbon is the theme of family, and what that means. Mick and Josef in this episode act so much like brothers, it just makes me hug myself with joy. Robert talks about his son being a miracle baby, just as he had been for his parents, and Mick does the math and realizes that Robert might be his son. Aside from that issue, Mick remembers his best friend, his best friend's wife, and the family that he broke up accidentally by falling in love with what he thought was Ray's widow. And Josef - of all people - expresses a regret (and he doesn't do regrets) that he never fathered children. And finally, at the end of the episode, Beth beautifully ties up the family theme by telling Mick what we Moonlight fans have all come to understand: Family's not just about DNA.

Mixed in and around the family theme is the child theme - which isn't necessarily about family at all. We discover that Beth has become something of an expert on child kidnappings... gee, I wonder why?


And then there's Medic Mick.



I would have loved to see more about this era of Mick's life, had the series gone on. What's Left Behind is a tantalizing glimpse into Mick's past, but it leaves us with many more questions than it answers. Maybe that's why this episode has inspired so much really wonderful fanfic.
Links:
http://www.imdb.com/title/tt1212043/
(No TV Guide episode discussion is available for this episode)
(No Wikipedia page is available for this episode)