The family's rejection plunges the monster into a fit of rage. But the beauty of the next day calms him. He decides to approach De Lacey again to try to make amends.
The monster's faith in old De Lacey shows its last gasp of innocence, saving it from the rage born of rejection.
But by the time the monster reaches the cottage, the De Laceys have moved out. He sees Felix terminating his lease with the landlord, and never sees any of them again. His last link with society destroyed, the monster gives in to rage and a desire for revenge. He burns down the cottage and heads for Geneva and Victor.
Its innocence and hopes of inclusion in society dashed, the monster is left with only pain, and naturally wants to hurt those who hurt it. That includes human society (symbolized in the house he burns) and its creator, Victor.
At one point along the way the monster saves a beautiful little girl from drowning in a stream, only to be shot by her guardian. It takes weeks for him to heal, and his suffering only feeds his anger and desire for revenge.
Another example of humanity's tendency toward prejudice, which only increases the monster's desire for revenge.
After a few weeks, the monster makes it to Geneva. There he encounters a young boy. Thinking the boy would be too young to be horrified by his appearance, and thus could be a companion for him, the monster approaches him. But the boy is terrified, and shouts that his father, a Frankenstein, will punish the monster. The monster becomes enraged at hearing the name Frankenstein, and strangles the boy. The boy dies.
Again the monster shows an innocent belief in man, this time that the young will be less prejudiced than the old. His hopes again dashed, coupled with the boy's connection to Victor, spur the monster to uncontrollable revenge. All this explains the murder of William Frankenstein (the boy).
The monster then finds a barn in which to spend the night, but finds a beautiful sleeping girl inside. Enraged that he is forever cut off from the delight of female beauty, the monster places a picture the boy wore and plants it in the girl's pocket.
The monster revenges itself on Justine (framing her for William's murder) because to the monster, she symbolizes the society it can never have.