Devidian Incursion

The Devidian Incursion was a brief conflict occurring in both 2409 and 2265. The Devidians invaded the Klingon-Federation Neutral Zone, planning to shift the residents in the zone to their own dimension. The danger they posed to the zone was removed by an investigating operative, foiling the Devidian plot.

Prelude
Investigation into Devidian activity began when a sizable force of Devidians attacked a True Way vessel - the Axon. The Axon and an escort attacked both the Federation and Klingons in their neutral zone. During the battle, the Devidians took the Axon's bridge, leaving very little of the crew alive. When either the Federation or Klingons won the battle, an operative was sent to board the True Way ship. The operative attacked both the True Way and the Devidians, ultimately killing the Phantasm commander on the bridge. Logs recovered from the Axon began an effort to investigate the Devidian presence. The operative then went to Drozana Station to help the operative Ze'mara; the operative discovered that the Devidians are likely have a malicious plan for the neutral zone considering the mysterious deaths and technical malfunctions that have occurred aboard the station. 

Investigation within Drozana (2409)
The operative entered deeper into Drozana Station, intending to access the Computer Core. The operative encounters Gein while moving towards the Computer Core. Gein kills a Bajoran as the operative conducts the search. Gein and a sizable number of Devidians are killed by the operative while searching for the Core. After Gein is defeated, the operative discovers dead, fresh bodies from the 23rd century. Upon reaching the Core, the operative defeats a Phantasm and discovers a Devidian portal. The operative scans the portal and temporarily leaves the station to analyze the scan. The analysis determines that the portal leads to the 23rd century. 

Investigation within Drozana (2265)
The operative enters the portal on foot. The operative either attacks or evades Federation security, eventually meeting Leonard McCoy. After helping McCoy treat several Federation officers injured by the Devidians, the operative discovers that Driffen's Comet is responsible for the Devidian incursion. With McCoy's help, the operative returns to 2409. 

End of the Incursion
The operative is tasked with stopping the incursion by destroying Driffen's Comet in 2265. After using the star in the Bepi 113 System to enter 2265, the operative goes to Drozana Station. Upon arrival, the operative disables the USS Reuben James. The operative enters the station and helps the Federation and Montgomery Scott defeat the Devidians on the station, as well as their commander, the Shrouded Phantasm. Once the station is secure, a fleet of Klingons led by B'vat attacks the operative as the operative attacks Diffen's Comet. B'vat tries to ram into the operative's ship, but Driffen's Comet is destroyed and the operative's ship is sent back into 2409 before this can happen. 

Aftermath
The destruction of Driffen's Comet ended Devidian involvement in galactic affairs; only brief technical issues and appearances on Drozana Station are the only evidence of their small presence after 2409.