I decided to change it to Sci-fi and Adventure since there's not that much Horror, hope you won't mind, anyway do not own Doom or Mass Effect, Doom belongs to Id Software and Mass Effect belongs to Bioware

Commander Shepard walked into the briefing room to see his team in there, all looking like they just woke up (except Legion)

"This had better be good battlemaster." Grunt said

"How does Batarians declaring war on the Alliance sound." Shepard replied

All of them looked at Shepard with confused and alert faces.

"The Batarians declared war on the Alliance, but how?" Tali asked

"Anderson said they attacked Mars City." Shepard replied

"Mars City? Isn't that owned by the UAC?" Garrus asked

"Yeah, about 6 hours ago, the Alliance had lost contact with Mars City, they haven't been able to raise them on any channels, and thanks to Udina and the rest of the consul, there's no way for the Alliance to send in a rescue, so Anderson asked us to go in and access the situation." Shepard said

"If the Batarians were to declare war on the Alliance, why not attack the Alliance Archives?" Thane asked

"Not a clue, guess it has something to do with the UAC being the biggest weapon manufacturer in the galaxy." Shepard replied "We'll be splitting up into two teams; I'll lead one team, but I a volunteer to lead the other."

"Shepard." Jacob said

"Yes Jacob?" Shepard asked

"Before I joined Cerberus I did some work on Mars City, so I know my way around some places." Jacob said

"Alright, I'll take Garrus, Zaeed, Miranda, Tali, Jack, and Legion. Jacob, you'll take Thane, Grunt, Kasumi, Mordin, and Samara." Shepard said

"Yes sir." Jacob said

"We'll be arriving there in 3 hours so get prepped, dismissed." Shepard said, some of his team saluted while others merely nodded and left. Shepard stayed there for a minute or two thinking to himself.

"The Batarians are declaring war at this time while the Reapers are on the Horizon; I just hope we can solve this conflict before the Reapers arrive." Shepard thought before leaving.

3 hours later….

"We're coming up on Mars City now." Joker said over the radio

"Alright listen up people, we're going to split up, Jacobs team are going in one side, while we go in the other, understood?" Shepard said, His team all nodded. The plan was that Shepard's and Jacob's teams would both take shuttles and go in separate parts of Mars City, right now they were in separate shuttles going in different entrances in Mars City.

"Shepard, I have detected a lot of unknown life signs in Mars City, some are human and alien." EDI said over the radio

"Any sign of Batarian life signs?" Shepard asked

"Strangely my scans have detected no Batarians in the base." EDI said

"Odd don't you think?" Garrus said "No Batarian life signs in the base, guess they must have found a way of cloaking themselves."

"We're coming up on a landing pad now." The shuttle pilot said touching down as Shepard's team all got out.

"Shepard this is Jacob, we've touched down and are making our way into the base." Jacob said over the radio.

"Good keep me posted, and good luck." Shepard said

"You too Shepard, Jacob out." Jacob said

"Alright, let's move out!" Shepard said as his team entered Mars City.