The frost flower "blooms" in the Arkansas Ozarks after the first hard freeze. The frost flower also provides a critical clue to solving a murder in A VALLEY TO DIE FOR.

 

In MUSIC TO DIE FOR the clue is a song!
 

 

Clue for A TREASURE TO DIE FOR is an old yearbook photo.

Clue for A WEDDING TO DIE FOR is a ghost bride dressed in red.

Clue for A RIVER TO DIE FOR is a cloud of dust.