Everything is perfect for Cynthia. For her and for her boyfriend, Arthur. Pakiramdam niya ay siya na ang pinakswerteng tao sa mundo dahil sa pagmamahal na ibinibigay nito sa kanya. And until their first anniversary came, everything is just so sweet, magical, and perfect. They were so inlove, just so much inlove that it even lead them to do it. It was the best part of their lives, specially to her. Pero unti-unting nasira ang kasiyahan niyang iyon, ng pakiramdam niya ay lumalayo na ang loob ng nobyo niya sa kanya. She doesn't know why. Hanggang sa nalaman niya na nagbunga pala ang pagmamahalang ginawa nila noon. She is excited to tell the news to Art. Naisip niyang baka bumalik ang lahat sa dati kapag sinabi niyang nagdadalang-tao siya. But those hopes faded when she finds out that Arthur leaves, he left her and their baby, without even telling them why or even goodbye. Six years had passed. Masasabing maayos na si Cynthia kasama ang anak niyang si Cielo, at ang kasalukuyan niyang nobyo na si Bryan, nalagpasan niya na ang mga sakit na napagdaan niya simula nang iwan siya ni Arthur. But what if destiny played with their lives again? Pagkatapos ng anim na taon ay makikita muli silang dalawa? At magkakasama pa sa trabaho? Is she willing to tell him that they have a child? Is she willing to accept him again? Or she will just do The Sweetest Sin, and that is to love him again.