Raskolnikov has it in his head to kill a mean and crooked pawnbroker, who happens to be a sixty-year-old woman. He's trying to get the idea out of his head, but he can't. The idea torments him to plan the murder down to the least detail. He knows exactly how many paces it is from his room to the pawnbrokers ("exactly seven hundred and thirty"), and even does a trial run of the murder. Part of him is convinced he could never kill and part of him is convinced that he must.
In this stage, the murdering side of Raskolnikov pushes the non-murdering side of him out the proverbial window. Suddenly he's carrying out his plan. Suddenly he's killing the pawnbroker with an axe, stealing her stuff, slipping in her blood, and alternating between panic and calm. Yet, he forgets to lock the door, and when Lizaveta (the pawnbroker's half-sister) happens upon the scene, Raskolnikov kills her, too.
Raskolnikov is completely confused after the murders. He doesn't know whether to turn himself in, kill himself, or just let things ride. He's caught in a vicious trap in his mind. If the murder served no purpose, if it didn't prove that he's a great man like Napoleon, then he's worse than he was before he killed and his life is meaningless. If he can just hold on, maybe he'll see that he was right, that killing Alyona wasn't actually a crime, but a deed to serve the greater good.
The complications in his mind lead him to act in complicated ways. He still does good deeds (mostly by giving money to desperate people), but he is alienating himself from the people who love him and playing dangerous games with the cops. As a result of his complicated actions, everybody around him is confused. They all suspect him, at least a little, but can't really believe he did it. At times, we have to remind ourselves that Raskolnikov is indeed the killer.
It feels like a little explosion when Raskolnikov finally confesses to Sonia. Even though he's been treating her like dirt for most of the book, this is the closest thing to a "real" love story we have to hang on to. Sonia thinks so too, and swears that she will "follow" him all the way to prison. True to form, he isn't sure if he wants her to or not.
Porfiry is sure Raskolnikov is the killer and he makes sure Raskolnikov knows it. Raskolnikov is sure everybody knows he's the killer and that, if they don't now, they soon will. The "suspense" stage of Crime and Punishment is kind of an intensified version of the "complication" stage. Raskolnikov doesn't know whether to turn himself in, kill himself, or run away somewhere. He can't just let things ride, because neither Porfiry nor Sonia will let that happen.
In this stage there is also the possibility that Raskolnikov will kill again. Both Porfiry and Svidrigaïlov are potential victims. Speaking of Svidrigaïlov, he provides lots of extra suspense in this stage. He's obviously capable of anything and his actions could have major impact on the outcome of the novel. They actually don't, but the whole Svidrigaïlov thing is mighty suspenseful while it lasts.
He almost doesn't do it. When he hears about Svidrigaïlov's suicide, he turns around and walks out of the police station, planning on doing who-knows-what (probably continuing the never ending debate in his head over whether or not to turn himself in to the cops). But, there's Sonia, sitting there in the courtyard of the police station, full of anguish and pain. We suppose he decided that it would be easier to just get it over with and turn himself in than to face Sonia without having confessed.
Sounds nice, doesn't it? Well, the narrator makes sure we know that things aren't going to be easy for Raskolnikov (he is in jail, after all). He's going to have to earn his happiness. Still, at least according to the narrator, Raskolnikov will eventually believe that life can be beautiful and sweet in and of itself, and that greatness can be found in plain and ordinary living, without any fancy ideas or Napoleonic aspirations.