What's in the box? It's a question both Deeks and NCIS: Los Angeles fans have been asking since last year, and "Three Hearts" may finally provide an answer.

Sam Takes On His Most Dangerous Undercover Mission Yet In 'Three Hearts'

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." Now that Kensi (Daniela Ruah) is back from Afghanistan, Deeks (Eric Christian Olsen) is taking advantage of her return and renewing his campaign to find out just what is inside the box that she gifted to him.

A new "Three Hearts" sneak peek showcases Deeks' lightning fast ability to change subject as the newly reunited partners go head to head with Van Halen trivia before the LAPD detective brings up the box (see video below). It doesn't look like Ms. Blye will let the answer slip anytime soon, however, and the Deeks may actually have to break the seal to satisfy his curiosity.

Deeks & Kensi To Pick Up Where They Left Off? What Will 'Three Hearts' Reveal About Densi?

Writers Dave Kalstien ("The Frozen Lake," "Tuhon") and Kyle Harimoto ("Merry Evasion," "Omni") have been keeping the contents of the box under strict lock down and even executive producer John Peter Kousakis couldn't give a hint as to what the cardboard exterior is hiding.

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

Find out more when "Three Hearts" airs April 15 at 9 p.m. ET on CBS.