As we see in William Godwin's Caleb Williams, it can be said it is the injustice of the law that drives Falkland to commit murder in the first place. One reason why Falkland murdered Tyrrel was Tyrrel's cruel treatment of Emily that eventually caused her death. However, Tyrrel was only indirectly responsible for Emily's death, so the law could not convict Tyrrel of murder. Under the law, the best that could be done was form an assembly of noblemen who voted to retract Tyrrel's title and privileges. However, sadly, such a punishment was insufficient to prevent a man as dangerous as Tyrrel from being violent again, as we see when Tyrrel later physically assaults Falkland. It is because Tyrrel insults Falkland by physically attacking him that Falkland decides the best way to defend his own honor as well as the late Emily's is to murder Tyrrel. Hence, it can be said the inadequacies of the law drove Falkland to take justice in his own hands by committing murder. Therefore, it can also be said that at first the law does not act in Falkland's.
However, it can also be said that the law does act in Falkland's favor by refusing to convict him of murder. In fact, when Caleb accuses Falkland of murder before the magistrate as an attempt to save his own reputation, the magistrate refuses to take the charge seriously, even saying that, as a magistrate, Caleb's accusation means nothing to him, unless Caleb "had [himself] been concerned in the murder [he] talks of" (Vol. III, Ch. XI). However, once released from prison, Caleb again goes to the magistrate to press murder charges against Falkland in another attempt to save Caleb's own reputation; this time, the magistrate takes Caleb's accusation seriously and has the now ailing and dying Mr. Falkland brought forth. Though Falkland finally does confess to the murder, again, the law fails to convict him since Falkland dies a few days later of due to his poor health.
Hence, it can be said that the law acts very ironically in Godwin's novel. The law acts ironically by first offering no legal means of protecting and defending Falkland against Tyrrel; then it acts ironically by failing to convict Falkland though he is truly guilty of murder. In behaving ironically, the law both acts against Falkland and acts favorably towards him.