"Affliction" is the fifteenth episode of the fourth season of the American science fiction television series Star Trek: Enterprise, and originally aired on February 18, 2005. The script was written by Mike Sussman from a story by executive producer Manny Coto. It was the second episode of Enterprise to be directed by Michael Grossman. The episode is the first of a two-part story, which concludes with "Divergence".

Set in the 22nd century, the series follows the adventures of the first Starfleet starship Enterprise, registration NX-01. In this episode, the crew investigate the kidnapping of Doctor Phlox (John Billingsley), and the ship is attacked by a new type of Klingon. Meanwhile, Phlox is taken to a Klingon colony to work on a cure for a plague whose effects include the disappearance of the Klingon's cranial ridges.

The episode sought to answer the question of why Klingons looked different in Star Trek: The Original Series than in other series of the franchise. It also introduced Section 31, originally seen in Star Trek: Deep Space Nine, to an earlier time in the Star Trek canon.

The episode featured a number of guest stars who had previous connections to the franchise, including James Avery who was in the running for the part of Worf in The Next Generation, John Schuck who played a Klingon Ambassador in two Star Trek films, and Eric Pierpoint who had appeared in several other episodes of Star Trek previously. Some of the standing sets were redressed to appear as the interior of the Columbia, and some scenes were filmed outside at the Paramount Studios lot in Los Angeles, California.

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