Hmmm. There's one thing in this:

"And as the Festival disintegrates around them, Ringan and Penny begin to suspect that Lady Susanna's death was not as simple as they've been told

that I think I need to change: it should be something about not being as simple or as straightforward as the song lyric suggests. IOW, I need to tie it into the song, which is the title.

For Ringan and Penny, though, there's a downside: Callowen is haunted, by the pretty young wife of a 17th century Leight-Arnold, killed by her husband when she's caught in bed with another man. What's more, her story is told in a famous traditional song, "Matty Groves". And the couple has already held two terrifying exorcisms for ghosts whose stories, true or false, are told in songs.

This time, it seems, there's no mystery for them to solve; the Lady Susanna's story is straightforward, and besides, Miles Leight-Arnold is very proud of his family phantom.

A few suggestions for clarity, mainly reorganizing your sentences:

For Ringan and Penny, though, there's a downside. The couple has already held two terrifying exorcisms for ghosts whose stories, true or false, are told in songs. And Callowen is haunted, by the pretty young wife of a 17th century Leight-Arnold, killed by her husband when she's caught in bed with another man. What's more, her story is told in a famous traditional song, "Matty Groves".

This time, it seems there's no mystery for them to solve; the Lady Susanna's story is straightforward, and besides, Miles Leight-Arnold is very proud of his family phantom. But from the first night, it becomes clear that Lady Susanna, harmless and tragic, is not the only spectre.

Something else is awake, moving through walls and nightmares, growing stronger as it feeds on Penny's sensitivity and on the very fear it creates: Andrew Leight, a man as twisted and violent in life as he is in death. When Penny is attacked and Charlotte, the daughter of the house, is injured, Lord Callowen gives Ringan and Penny an ultimatum: get rid of Andrew Leight, but leave Lady Susanna's ghost untouched.

But I like Amy's suggestions even better.

Bev, niiiiiiiiiiiice.

Damn. My brain is backstage at Madison Square Garden right now, not in Hampshire. Very tricky trying to focus.

Actually, I want to use yours, end it with Amy's, and take part of connie's suggestion about the Callowen info. Gimme a minute...

edit: except "spectre". I hate that word, and never use it.

Well, I take issue with the fact that Susannah isn't "alone." I don't think she IS with Andrew. I'm not overly fond of spectre, it just wasn't ghost again.

OK, howsabout this?

For Ringan Laine, an invitation to perform with his band at the Callowen House Arts Festival is a mixed blessing, especially when he's asked to bring his longtime lover, actor-producer Penny Wintercraft-Hawkes, along as an honoured guest.

The Festival, held every year at Lord Callowen's stately home in Hampshire, is as prestigious as it gets. Artists perform by invitation only, to a handpicked audience. For two weeks, the fortunate participants enjoy every luxury that Callowen House, family seat of the Leight-Arnolds, has to offer.

For Ringan and Penny, though, there's a downside. The couple has already held two terrifying exorcisms for ghosts whose stories, true or false, are told in songs. And Callowen is haunted, by the pretty young wife of a 17th century Leight-Arnold, killed by her husband when caught with another man. What's more, her story is told in a famous traditional song, "Matty Groves".

This time, it seems there's no mystery for them to solve; Lady Susanna's story is straightforward, and besides, Miles Leight-Arnold is very proud of his family phantom. But from the first night, it becomes clear that Lady Susanna, harmless and tragic, is not the only ghost.

Something else is awake, moving through walls and nightmares, growing stronger as it feeds on Penny's sensitivity and on the very fear it creates: Andrew Leight, a man as twisted and violent in life as he is in death. When Penny is attacked and Charlotte, the daughter of the house, is injured, Lord Callowen hands Ringan and Penny an ultimatum: get rid of Andrew Leight, but leave Lady Susanna's ghost untouched.

And as the Festival disintegrates around them, Ringan and Penny begin to suspect that Lady Susanna's death was not as simple as the song lyric suggests, and that the truth may expose a four-hundred-year-old lie with implications far greater than a husband's betrayal.

Works for me! And now, back to the Garden?

I don't think she IS with Andrew.

No, she's not "with" him. But she's his focus. She's what he wants, chases, won't allow to rest. She's the reason he's still there.

And "ghost" is fine; it's a ghost story, after all...

Yep, back to the Garden (Joni Mitchell moment just went through here...)

Sorry I disappeared -- it was time for Princess Stinkypants' nap.

OK, howsabout this?

Looks good. I love writing copy. It's a word puzzle -- you have to include X number of details in Y number of words, for maximum "must read this!" effect. (And that's the only math I like to do.)