What's in the box? It's a question that has plagued NCIS: Los Angeles viewers since season 4, and the mysterious package could return once more in season 6.

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Patience is a virtue, and Deeks (Eric Christian Olsen) appears to have it in spades. Originally delivered to Kensi (Daniela Ruah), The box arrived in the Special Operations office during last season's "Kill House," before moving sitting in the background of the bullpen from "Red: Part One" until "Three Hearts." Kensi passed the cardboard enigma off to Deeks, but the LAPD detective refused to touch it until Kensi cut the tape last season.

In a Russian nesting dolls twist, the box contained yet another cardboard container, one which Deeks has yet to unseal. David Kalstein, the man behind both "Kill House" and "Three Hearts," might finally provide an answer to the UPS riddle in a potential Densi-centric episode later this season.

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For now, however, the contents the package remains squarely in the diabolical mind of series creator Shane Brennan.

"The only person that knows what's in there is [Executive Producer] Shane Brennan, so I am as emotionally invested as everyone else," Olsen told Entertainment Weekly, joking that he would like to break in one night and find out the truth for himself.

Find out more when NCIS: LA air Mondays at 10 p.m. ET on CBS. Click the video below to see a preview for the series next episode, "The 3rd Choir."

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NCIS: LA, NCIS: Los Angeles, CBS, Television