The main conflict in 'Return to Sender' revolves around Lin Townsend's struggle with forgiveness and her unresolved feelings towards Nick Pemberton, the father of her son, who abandoned them years ago. Lin's encounter with Nick brings back old wounds and challenges her ability to move forward.

Return to Sender portrays single motherhood through the character of Lin Townsend, highlighting her resilience and determination. Despite being abandoned, Lin builds a loving home for her son, Will, and overcomes numerous challenges to provide for him, showcasing the strength and sacrifices of single mothers.

Return to Sender explores themes such as forgiveness and second chances, resilience and single motherhood, and the enduring power of love. The novel delves into the complexities of forgiving past betrayals, the strength required to overcome adversity as a single mother, and the lasting impact of love in various forms.