The mystery of 'The Box' may soon be coming to an end on NCIS: Los Angeles.

Kesni Drops Off The Grid & Sam Heads Into A Trap On 'NCIS: LA'?

A gift from Kesni (Daniela Ruah) to Deeks (Eric Christian Olsen), the box arrived in the Special Operations office during last season's "Kill House," and it has been collecting dust, unopened, in the background of the bull pen since "Red: Part One."

Nearly a season and a half after it was introduced, it looks like the box will be picked up once more in episode 21, "Three Hearts." Penned by Dave Kalstein ("Kill House," "The Frozen Lake") and Kyle Harimoto ("Merry Evasion," "Omni"), the episode has been called a "game changer' and will be signal Kesni's second episode back in the states.

Will The White Ghost Return When Eric Enters The Field To Save Russian Missiles On 'NCIS: LA'?

"The Box E520(21). What's in it? @davekalstein &@Harimoto won't tell ME! #staytuned Densi connections continue 2 entwine! #NCISLA," tweeted executive producer John Peter Kousakis.

While it appears the box will be featured in "Three Hearts," there is no guarantee that Deeks will actually open it.

"I can tell you that later in the season, [Deeks] takes the box down and puts it on his desk and stands over it and he may or may not open it," said series creator Chane Brennan, according to TV Fanatic.

Do you think viewers will find out the contents of the box? Sound off in the poll below!

NCIS: LA airs Tuesdays at 9 p.m. ET on CBS. Click the video below to see a preview of the series' next episode, "Between the Lines."