In 2368 an archaeological team digging under San Francisco made a remarkable discovery - the head of Lieutenant Commander Data was found amongst some 19th century artefacts. The conclusion was obvious - at some point in the future Data would travel back in time to the 19th century, where his head would become severed.

Shortly afterwards, the Enterprise was called to Devidia II where it was discovered that the natives of the planet were travelling back in time to 19th century Earth in order to drain neural energy from the inhabitants in order to use it as a food source. The Devidians existed slightly out of phase with our time, making it difficult to observe or interact with them. The Devidians utilized a snakelike alien called an Ophidian to open a portal across space and time by irradiating it with the proper energy.

Many of the Enterprise's officers travelled through the Devidian portal to combat the threat, but this led to some awkward consequences. Samuel Clemens, the writer known as Mark Twain, was accidentally sent into the present and beamed aboard the Enterprise. Captain Picard, on the other hand, was stranded in the 19th century while Data fulfilled his role by having his head severed.

The Enterprise crew were successful in rejoining Datas body to the 19th century head, and sent Mr. Clemens through the Devidian portal. Picard was able to return also, and shortly afterwards the Enterprise used modified photon torpedoes to destroy the site from which the Devidians were operating. Since this time there have been no further incursions.

Temporal Investigations decided after detailed scanning that leaving Mr Clemens with knowledge of the future created too great a risk of altering the timeline. A team was sent into the past, where they deleted the appropriate memories from Mr Clemens. Temporal Investigations has also set up a temporal scanning system on Devidia II to watch for any further attacks by the local inhabitants, but so far none have been made.