Mark is grieving for his girlfriend, Kiera. She committed suicide and, unable to find closure and move on, he decides that he needs to find out why she did it. And so, the film begins with Mark drinking a strangely-coloured substance. Soon after, Kiera appears, confused as to why she's here again. Shocked, Mark explains his intention, and that he summoned her spirit here to do it. She refuses, but Mark explains that the substance he consumed also allows them to travel into their memories.

The first memory is from many months ago, with Kiera learning she's pregnant. It's hopeful, and she and Mark are very excited. However, on the desk she's sitting at, she keeps a strange list of milestones of their relationship - "first date", "second anniversary", etc., which creeps present-day Mark out. Before he can ask present-day Kiera what its purpose is, they enter the next memory.

The second memory is more recent. It shows Mark waking up in bed and noticing Kiera sat on the edge, grieving at the stillbirth of their child. He attempts to comfort her, but she refuses it. Mark, suspicious of Kiera's sinister behaviour, then notices torn fragments of paper - ripped pieces of the strange list Kiera had been keeping. She tells him to go back to sleep, and he reluctantly does so. Unknown to him, there's a knife in her lap.

Outside of the second memory, Mark asks Kiera to explain her strange, unsettling behaviour, but she says he won't like the answer. He doesn't care - he needs to know - and so they enter the third memory.

The third memory takes place a few hours before the second, in a hotel room, where Kiera invites a stranger inside. It seems as if she went there to cheat on Mark, but when the stranger is stabbed three times in the chest, Kiera's murderous nature is revealed. As they watch the Kiera within the memory clean up the crime scene, present-day Kiera explains to Mark her motivations: that killing strangers brought her no pleasure, so she decided to kill someone close to her instead - in this case, Mark.

The strange list from earlier acted as a checklist of how close they were in their relationship, and once the list was completed (and, therefore, they were the closest (emotionally) that they could be to one another) then she would kill him. But, when their pregnancy didn't go as planned, "Have kids" was unable to be achieved and thus the list could never be completed. Her goal would forever go unfulfilled. And so, there was nothing left to live for. She chose to end her own life.

Back in reality, Mark reels from this horrible realisation. Then, as the effects of the potion begin to wear off and Kiera's spirit begins to disappear, he asks why she spared him. She could've killed him anyway, even if the list couldn't be completed, so why didn't she?

She doesn't answer the question outright, evading it, but she essentially admits that it was because she loved him - she only ever wanted to kill him because she loved him, but it was because she loved him that she couldn't bring herself to do it. One final, tragic, act of kindness at the end of her corrupted life.

With their relationship crushed, and Mark's fond memories of their time together forever tainted, Kiera disappears and leaves Mark alone again, back where he started.