The song was originally sung by Hinata Haruhana. Like it's answer song Nazotoki, it was illustrated and composed by the same people.
The song was based on Hinata Haruhana's story Umi wa sono nazotoki wo nozomu noka? (海はその謎解を望むのか?), however, the "full" version of Nazotoki uploaded on June hinted it was a "different" version, similar, but not the same. This applies to Nazokake as well.
A novel adaptation of the song "Nazokake" written by Hinata Haruhana and illustrated by Yon published from Poplar Pocket in July 2014, is also loosely based on this story; with a similar set of characters, the main difference being the two main characters "Kurono Rin" and "Shirohane Len". A hardcover version of the novel is available later in April 2015.
This song is in the girl's point of view. She wondered why the detective kept on hurting himself, thinking he can protect someone.
She then talks about the first mystery, saying there were actually two wine glasses, and even if he didn't die by the poison in the wine, the man would have died by 'the knife(most likely the girl's knife).'
While listening to the detective, she kept on thinking that everything was a lie and doubted that he was the 'detective'. The girl tried taking a shot at the riddle, saying "'He' could only kill them one by one, but still couldn't be the culprit" ('One by one' may refer to the group of people falling down to the ocean)
The girl tried to 'accidentally' kill the detective, and gave her answer to the detective's question: "Who is the culprit?" and replies, "The culprit is not you."
The video then shows a building on fire, and the one-armed detective standing on the staircase. She said the detective's arm was used to play the piano, but the detective tried to 'save' the girl.
She said that she will solve the riddle, and the detective. Whoever is involved in the mystery, the girl will trap them; "Welcome to our world"