Here's the spoilers for what will happen on Days soon; these are almost always accurate. Don't read if you like to be surprised! Scroll down for some rumors. Keep in mind that rumors only come true about half the time.
Hope realizes that Marlena could very well be the killer, but John continues to defend hsi wife.
John goes to Celeste for help, and later visits the priest.
Celeste gets and realizes who the next victim is.
Alice finds Doug's blood written note with Marlena's name on it.
Marlena realizes that Alice has evidence against her! Tom's ghost warns Alice.
Marlena is about to kill Alice, but before she can, her victims' ghosts chase her off! Alice makes a call, but who?
Roman's ghost gives Kate instructions on what to do.
Abby finds a mysterious belonging of Patrick's.
Belle and Sami have a girl's day out.
Shawn is delayed getting to Belle because of a car accident. He has plans to propose to her.
John races to confront Marlena.
John and Sami have a confrontation, and Sami thinks he will kill Marlena.
John and Marlena struggle on the penthouse terrace. Meanwhile, Sami is watching and thinks that John and Kate are the killers, trying to set her mother up.
When Marlena confronts Alice, Alice urges her to get help.
The victims' ghosts appears to Alice.
Jennifer begins to have pains, and Patrick continues to stay with her.
Jan plans to murder Belle!
The killer storyline will last until December 2004.
RUMORS
Marlena's victims all not only come back as ghosts, but they get their revenge on her.
Alice will be the final victim of the serial killer storyline! (the spoilers above point to this, but it has not been officially confirmed yet)
One of the next victims will be Bo (remember Celeste told Hope that she'd have a new wedding ring, and Caroline's ghost warned Bo there was danger ahead for him?).
Greta returns to Salem and falls for Brady.
Belle may be recast.
A couple rumored twists about the storyline:
Marlena simply went nuts; no other reason for the killings
Marlena has always been "bad", she's always worked for Stefano and it's just coming out now
This whole storyline is not really happening. The characters are not really dead; this is simply a book that one of the characters is writing or a dream that someone is having (someone even suggested that Sami is playing a game of SIMS)
Celeste, Shawn, and Lexi will all be Marlena's victims. Hope, John and Bo realize that she's the killer, and when they go to confront her, Marlena tries to kill Hope. In order to rescue Hope, John has to kill Marlena, thus fulfulling Celeste's prophecy from a while back that John will kill Marlena.