[TOMT] i need help finding this movie!

hi everyone back in 2014 ish i watched a movie with my sister and i just now thought of it and cannot remember for the life of me what it’s called. i tried google but its hard to find anything about it because all i remember are general details that almost every movie have

idk if it released on or around 2014 but i put that year in anyway to see if it’ll get us closer to the answer.

so the middle of the movie, one of the kids (i think maybe in their teenage years. all friends or siblings) gets kidnapped by i think a lady that seems almost ethereal. he gets taken to this lake that has an interesting name. his friends are trying to find him and they get to a cave or cavern i think which is where they thought he would be. they find a letter that he wrote to them basically telling them he was fine and he chose to go along with this. but theres a spelling mistake. one of the kids points it out and the other is like “so what?” and the first suspects something, because the kidnapped kid is really particular about spelling and grammar. i think he’s real smart or something. they keep reading and the first kid notices more and more spelling mistakes and is like “okay this is not a coincidence”. they take the missing letters from the misspelled words and it spells out the name of the lake and that’s how they find him.

i think there’s butterflies or something to do with butterflies too?? and i’m pretty sure the kidnapped kid and the kidnapper are on a boat on the lake and she starts floating them away or something