Sasiwimol is an extremely successful director and an open-minded mother who maintains a close and easy-going rapport with her teenage son, Wang. However, even someone as understanding as Sasiwimol is left shocked and bewildered upon learning that Wang is about to experience his first feelings of love and has fallen for the one and only Inthawut, a long-time trusted friend and contemporary of hers. In an instant, life, love, friendship and trust are all put to the test as the three souls find themselves converged by an intricate "line" that is set to forever alter the close-knit bond between a son, a mother and her beloved friend.
Wang, who is on the verge of turning 20, has spent most of his life away from home growing up in a boarding school. Having lost his father to a tragic accident, Wang is the apple of his mom Sasiwimol's eyes, with the two almost sharing a brother and sister like relationship. In a strange twist of fate, one day, as Sasiwimol and Wang are to scout the filming location for Sasiwimol's latest drama, they end up losing their way and find themselves near a secluded mansion in the middle of the woods only to be greeted by Inthawut, a long-time and dear friend of Sasiwimol. However, little do they know that this unforeseen reunion is only the beginning of a chain of events that is set to forever alter the relationship between the three souls.
After her triumphant win at the award ceremony, Sasiwimol returns back to In's to face a grown-up and responsible Wang who's finally agreed to continue pursuing his further studies. And while Sasiwimol is happy to see the positive change in her otherwise rebellious son, little does she know that she's in for the shock of her life when Wang suddenly reveals what he feels for In.
Following the broadcast of Sasiwimol's award ceremony, Wang continues to ask In more questions about his father's past. Filled with a deep sorrow in his heart, In finally goes on to reveal more details and secrets about him and Siam that has never confessed to anyone before. But the more that In seems to reveal to Wang, the more he feels guilt-ridden about Siam's passing.
Upon receiving Wang and Sasiwimol, In prepares them a lovely feast and the three sit down together for a chat with In revealing past stories about him and Sasiwimol to Wang. However, as a result of Sasiwimol's drunken state, Wang and his mother get into a heated argument and In has to hurry to appease the two, thereby finally learning the truth behind Siam, her husband's death from Sasiwimol.
After a night of heated conflicts, Wang, upon In's suggestion, apologizes to his mother and the two finally reconcile and make amends. Elsewhere, Sasiwimol at her end decides to throw in a special, surprise celebration for Wang's 20th birthday at In's. After the party, the three sit down to play Truth or Dare, and when faced with the question about who his idol is, In's response seems to be hiding something….
Upon getting his leg injured in an accident, Wang decides to attend to and take care of In until he gets better. As the two increasingly begin to spend time with each other, they gradually open their hearts and talk about their past with In revealing stories about him, Siam and Saiwimol and their college days to Wang and Wang confiding in In about his supposed boarding school romance.
With Sasiwimol having to attend an awards ceremony, Wang and In are greeted to some time for themselves. In their short time together, the two become the best of friends talking about anything and everything under the sun. However, despite sharing almost everything with each other, Wang is still unable to get the truth behind his father, Siam's death. However, one sudden night, In wakes up to the memories of his beloved former acquaintance, Siam.