Chapter five, of Mary Shelley's Frankenstein, proves to be the turning point of the novel. It is from this point forward that Victor's seeking of Forbidden Knowledge proves to be tragic.
Chapter five opens on a "dreary November night" where Victor's toils see completion. Unfortunately, chapter five is where all of Victor's's hopes for satisfaction are dashed. Upon "awakening," the Creature's agitated motion and hideous appearance frighten Victor. Victor even goes as far as to call his creation as catastrophic.
After the Creature looks at Victor, with its yellow eye, Victor rushes from the room and begins pacing his flat. Physically exhausted by the pacing, and mentally exhausted by the catastrophe of months of labor, Victor collapses in sleep. During this sleep, Victor dreams of both his mother (deceased) and Elizabeth (who dies--offering the reader foreshadowing of what is to come).
Upon waking from his nightmare, Victor sees the Creature looking upon him. Frightened even more, Victor rushes from his flat. Again agitated to the point of exhaustion, Victor continues his pacing through morning in a church.
Once daylight breaks, Victor emerges from the church and begins walking the streets of Ingolstadt. Upon seeing the inn, Victor pauses before it. Amazingly, Henry Clerval (Victor's best friend) has arrived in Inglostadt. After exchanging short formalities (what is happening at home), Victor takes Clerval back to his flat.
Worried that the Creature may still be at the flat, Victor rushes in so as to check to make sure the Creature has left. After insuring that the Creature has left, Victor rushes backs down to Clerval to bring him into the flat.
During a breakfast, served by Victor's servant, Clerval asks Victor what is wrong with him. Victor, refusing to answer and thinking he sees the Creature, becomes uncontrollable. With Victor falling into an immediate illness, Clerval nurses him over the course of the remainder of the chapter. The chapter actually closes with Clerval asking Victor to write to his family and a letter from Elizabeth waiting to be read.
In order to show a different perspective, I have linked the ENotes summary of chapter five.