Is a plaintiff liable in tort for failing to take affirmative action to protect another?

The general rule is that a person who has not created a peril is not liable in tort for failing to take affirmative action to protect another unless they have some relationship that gives rise to a duty to act. (Williams v. State of California (1983) 34 Cal.3d 18, 23, 192 Cal.Rptr. 233, 664 P.2d 137.) However, one who undertakes to aid another is under a duty to exercise due care in acting and is liable if the failure to do so increases the risk of harm or if the harm is suffered because the other relied on the undertaking. (Ibid.) Section 324A integrates these two basic principles in its rule.