In NCIS Season 11, Episode 6 ("Oil and Water"), Gibbs' team will metaphorically dive deep to solve an oil rig explosion mystery. But that is not the only whodunit in the show. There's a prankster bugging everyone - including Gibbs (Mark Harmon) himself! It seems the viewers will have a little bit of fun and laughter as the show transitions after the exit of Ziva David (Cote de Pablo).

Spoiler alert: This feature contains minor spoilers from "Oil and Water," Episode 6 of the eleventh season of NCIS.

Here are the highlights of In NCIS Season 11, Episode 6:

In the previous episode, Tony DiNozzo (Michael Weatherly) rants about the fact that no one in the NCIS would mention Ziva David anymore. The old DiNozzo being somewhat gone, Gibbs' team has been generally unwell since Cote de Pablo left the show. Things shake up a bit this week (Oct. 29 episode).

- NCIS works alongside the Coast Guard Investigative Service (CGIS) to find out the cause of an explosion on board an oil rig.

- A mysterious prankster pulls some Halloween tricks on the team, giving Tim McGee (Sean Murray) a more difficult time at work. Even Gibbs gets pranked!

- Guest stars include Diane Neal, who plays Special Agent Abigail Borin. Leslie Hope returns as SecNav Sarah Porter.

Who is Ziva David's Replacement?

The CBS network, as well as NCIS showrunner Gary Glasberg, affirms that Cote de Pablo is irreplaceable at NCIS. But Glasberg says he's "adding" more characters as needed. Still, for the viewers, the next to take up Ziva David's desk is her replacement.

Emily Wickersham ("Sopranos") will be appearing in a November episode for a potentially regular role. Reports indicate she has signed on for three episodes, as Ellie Bishop.

NCIS' Abby, Pauley Perrette, teases some brilliant moment with Diane Neal in this week's episode. She said on Twitter, "@DianeNeal is back and she ROCKS IT!"

VIDEO: A Sneak Peek into NCIS 11x06, 'Oil and Water'

NCIS Season 11, Episode 6 ("Oil and Water") airs Oct. 29 in the U.S. network CBS. NCIS fans in Australia, can catch the show on fast track on TEN. The next episode ("Better Angels") will have Ralph Waite in a recurring role as Gibbs' father.

More 'NCIS Season 11' and TV Guide Features:

NCIS Season 11 Spoilers: Tony Misses Ziva David; Cote de Pablo Replacement in November; Abby Now Likes Delilah? [READ]
NCIS Season 11 Spoilers: Mike Franks 'Returns' in Episode 4; Cote de Pablo Replacement is Emily Wickersham? [READ]