Plot vs. Character What Do You Think?

I've been thinking a lot about plot vs. character lately.  My most recent example is the Castle over-arc of Beckett's mother's murder.  When I wrote on Tuesday that I loved the step forward we'd taken in Beckett and Castle's relationship and I didn't really care about the mom's murder stuff tacked on at the end, I started to analyze that. 

Setting aside the fact that I believe the writers have drawn the murder "mystery" out too long and provided such clues as "you don't know who you're dealing with,"  and "this is so much bigger than you imagine," without actually giving any backing so it seems silly now, I think that the original premise was good.  But the reason I tune into Castle is for Beckett, Castle, Ryan and Esposito.  And when I thought back to my favorite books I realized that while I loved a great plot, it really was about loving the characters for me and wanting to know more about what was going on in their lives and how they were going to deal with it.  (Another great TV show that did that was 24.  The plots were fast-moving and sometimes silly (hello, remember the cougar and Kim? Haha, good times)  but we tuned in to see what was happening to Jack Bauer and how he was dealing with things.

When I brought this up to an author friend of mine, she disagreed with me to some extent.  "Without a great plot, who cares about the characters?" she said.  So, then I thought about how I would feel if we just tuned in to see the mystery of the week for Castle, or maybe I just read about Sadie Hoffmiller's neighbor being murdered without learning anything about her kids, her boyfriend, or anything else.  And I decided that for me, the characters are the most important thing because if you don't have likable, relatable characters, you don't have anything to make the reader care about the plot.  You could have the greatest plot in the world, but if you have flat characters, I don't believe you will find an audience that will care.  I think audiences like to be transported to someone else's life, to see their trials and how they're dealt with and for a moment, live vicariously.

I know I could do better at this in my own writing.  I like to think I write stories with great twisting plots that take people away to foreign places and hurtle them through events intertwined with people that leave the reader breathless.  Now I'm thinking I need to dig deeper into my characters and show how, in any given situation, my hero is worth rooting for. 

What do you think?  Plot or character?  How can you balance both?