All Hands on Deck (Six of Clubs)

In this crossword puzzle, you have to find 5 sets of quartets (each a group of four based around a specific theme). 3 of each group will be in the puzzle, and taking the fourth letter from the fourth member of each group will give you your keyword.

Solutions
Explanation of Group A Four Horsemen of the Apocalypse

Members of Group A War Pestilence Famine Death (hidden clue)

Explanation of Group B Four Humors (or fluids associated with humors)

Members of Group B Phlegm Melancholy Choler Blood (hidden clue)

Explanation of Group C Four Cardinal Directions

Members of Group C West East South North (hidden clue)

Explanation of Group D Four Elements

Members of Group D Air Earth Fire Water (hidden clue)

Explanation of Group E Four Seasons

Members of Group E Autumn Spring Winter Summer (hidden clue)

Keyword solution The fourth letter of each hidden clue spells out TOTEM