What was the event/device that sent Victor back to Geneva? |

While Victor plans his return to Geneva for some time, he & Henry are forced to remain in Ingolstadt during the harsh winter. However, a letter arrives from Alphonse (Victor's father) explaining that Victor's younger brother William has been killed. This initiates the friends' rush home.

As soon as he reads the letter, Victor suspects his creation as the murderer, but he keeps this secret as his own. He fears what harm this creature may bring against humanity (and his own family in particular). Yet he never discusses this with anyone, nor brings it as evidence to Justine's trial. Instead, he returns to Geneva and mourns with the rest of his family, even though he could end both their & innocent Justine's suffering by confessing.