Talking to the Dead follows Kate, who's husband Keven suddenly died. In the aftermath, she realises that she's lost a chunk of her memory, and she hear's Kevin's voice everywhere. Is she going insane? The answer is - yes. But that's the whole point of the story.
As the story progresses, you can see that Kate was actually in an emotionally abusive (and starting to get physically abusive) marriage. It's clear to the reader that she was better off with Kevin dead. And while I normally don't wish characters dead, I only wished Kevin stayed alive for him to get what he truly deserved. He (and Donna) are truly two of the most awful, self-centered people in the whole book.
Apart from Kevin's betrayal, Kate also has to deal with Heather (her sister). This may be quite spoiler-ish, but I have to rant about it. I can't believe what a terrible sister Heather is. I can understand her being friends with Donna and unwittingly feeding her information when she didn't know any better, but when she found out Donna's true nature, how could she remain friends with her? She seems to have a complex - she has to appear right no matter what.
So yeah, I have a lot of sympathy for Kate. I think she's been treated really unfairly. But at least the ending is positive. No, she isn't magically cured and free from anger, she's getting there. She's making baby steps, and with God's help, she's getting rid of the hurt and the pain inside.
Allow me to insert an appropriate video here: It's called "Healing Begins" by Tenth Avenue North:
An excellent book dealing with mental illnesses, faith, betrayal and groping for the way back after falling hard on the concrete.