Alternative

Conventions used in all adventure scripts: Normal text can safely be told to your players. Bold text is explanatory notes which only the GM / Narrator should see. To read more about the planets, races and tech involved in this adventure, follow the links throughout the script. Names are mostly left open to be described at the GM's discretion.

Introduction

Following the Captain's beheading in the last episode, the ship is sent to dock for refits and to await the new Captain. The Crew do not know much about her, save she is a woman and has a reputation for stringency. When she arrives at the dock, she lives up to her reputation. However, as soon as the ship leaves dock, she loosens up considerably.
[the Captain has been consumed by an alien entity, intent on using her influence to take control of the ship. The aliens cannot interact physically with objects in our dimension, so rely on the Captain to remove the Crew for them. She will encourage the Crew to spend more time in the holodecks, which have been rigged to cause various mind-bending effects on the Crew. After the following troubles, telepathic characters will have flashes of seeing the alien 'inside' the Captain, and can cure her and the Crew].

Welcoming Party

Soon after the ship leaves dock, the Captain invites all the important Crew to a welcoming party in Holodeck 1. The holodeck is set up as a Roman villa of the period, roughly, 100BC. Furnishings are lavish, food is rich and plentiful and beautifully exotic women wander the corridors. The Captain announces she is to make a speech; in it, she thanks the Crew for their warm welcome and suggests that possibly her reputation precedes her. The party continues for several hours, before finally an irate Andorian crewman suggests it is time to leave.

The First Sign

As the Duty Crew take their turn on the bridge, manning a patrol of the sector, the Doctor recieves an urgent call for assistance in a crewman's quarters. The examination reveals the Betazoid Science officer is suffering from severe shock, cause unknown [he was the first to suffer the side-effects of the aliens influence]. He is taken to Sickbay for observation, while the Crew return to normal duty.

Time Off

When the shift finishes, the Captain suggests the Crew have worked hard and deserve a break, in the holodeck. Although the crew look surprised at the offer, none refuse. One officer invites the Crew to take a role in his new holonovel, 'Que'mkka RyT'qq', a Klingon epic. In this, each Crewman plays the part of a warrior on a journey to avenge the deaths of his family. One of the officers involved is Betazoid. Shortly into the journey, she keels over, writhing in agony. The Doctor diagnoses the same symptoms as with the previous Betazoiod.
The Captain orders a scan of the ship, but this reveals nothing, as does a biological scan.

Life Goes On

The Captain orders the Crew to get to the bottom of the problem, but first, to get away from it all in the Holodeck. This time some crewmen politely refuse, saying they would prefer to help save their fellow crewmembers. The Captain looks surprised for a second, then laughs and says it was a silly idea, of course they should get to work [instead she will concoct a problem in the Holodecks to get the senior officers in there, under the warping influence of the aliens]. The problem conveniently requires the skill of all the senior officers, or all the Crew members.

Under the Influence

After half an hour in the mysteriously malfunctioning holodeck, all the Crew members begin to experience unusual feelings. First sickness, then dizziness, then nausea, and finally a thumping headache, varying in order for each Crewman. Leaving the holodecks makes no difference. As they exit, probably towards Sickbay, three crewmen charge past, the first apparently fleeing from the two behind, who are wielding phasers. It is then that the real effects begin. Either choose or roll on the table below to determine each Crewmans symptoms...

D6 Roll...
1 : Paranoia
2 : Schizophrenia (especially funny in mixed-race characters)
3 : Aggressiveness
4 : Flashbacks (have this character write down two or three past events for you to refer to)
5 : Impulsive behaviour (far worse than the -1 Disadvantage)
6 : Foresight (random near-future events)

The Crewmembers begin to experience their chosen 'illness'. From here on, it's up to you how the game progresses. I would have a few random encounters with similarly-plagued crewmen, a run-in with a pitched battle stretching across Deck 4, a chase with a paranoid schizophrenic, or something like this, at least one or two scary encounters.

Discovering the Aliens

Any telepathic Crewman will have occassional flashes when looking at the Captain. For a second, she appears as a skeleton-like creature, then the vision disappears. This vision shows the alien inhabiting the Captain. At first suggest to the players that it is just something to do with their illnesses, then if they suspect something is amiss with the Captain, let them get it right. The aliens can be scanned using a modified polaron beam, set to low-res scan, which will show up the alien. Further scans show that the alien is close to killing the Captain as its need for her diminishes.

Purging the Alien

The best way to remove the alien is to restrain the Captain then flood her body with ionized tachyon particles. The Crew can eventually discover this, despite their various madnesses. As for what happens next... well, their complaints will slowly disappear as the aliens lose their influence, but it would be funny to have one character develop nightmareish flashbacks to his days of crazed rampages in the turbolift... it's up to you.