New 'day' came to the Citadel. Meanwhile Shepard and his crew were on the mission on Tuchanka, Daniel was resting after being given the antidote. His rest was interrupted by the light coming from the opposite window. As his eyes opened, he saw blurry blue silhouette sitting in the room. Once his eyes focused, he recognized David Anderson sitting in there. Daniel rose up using his hand.

"Captain Anderson?" he asked hoarsely.

"Good morning, if we can say that on permanently lit Citadel!" Anderson smiled.

"Uh… is there some problem, captain? I don't think you would come only for chat."

"Maybe you're not right, Daniel. I came to talk. Nothing else."

"Yes? About what?"

"I wanted to give you a support. As far as I tried to remember what happened in last week for you, it was much and yet many things are ahead."

"What do you mean?"

"Well, waking up in new environment, far from Earth, between alien species. Becoming soldier in a short time span, almost getting killed in battle, finding and losing love, being experimented with Cerberus, getting saved from committing suicide and now you are part of our war between Reapers. Daniel, honestly, you've made a big progress here in such a short time span. And when I think that Alliance wanted only to destroy project Soma… We underestimated you."

"Yeah… maybe. I'm lucky that there are still people who are supporting me."

"I know, almost everyone from Shepard's crew says you're getting along… well except for Javik. That prothean seems to be quite mad at you."

"I… don't feel like you're here only to tell me how much progress I did. What is going on?"

"Alright Daniel. I just want to say, hold on. The war with Reapers is gonna be hard but once it's over, it will be up to you which way of your life you'll head. You can either stay with us, join the Alliance and fight with Shepard or lead your own ship. Or you will retire and live your own life… possibly that other option is going to be more pleasant for you."

"Yeah, it sounds… but somehow I don't feel like seeking for peace anymore. Time spent with Shepard and others taught me something and I realized that army became something that will lead me through life."

"I didn't want army to be your master, Daniel. I have an offer for you before Shepard comes back."

"What offer?"

"Intergalactic association of education agreed to follow human system of university curriculum. Students of local university on the Citadel are studying calculus. Are you familiar with that?"

"Yes, I taught it few times on universities. Why?"

"Why don't you use the opportunity and relax while you do the lecture?"

"You want me to teach calculus for intergalactic species?" Daniel had to smile.

"It's just offer. They already know about you from me. Just tell me yes and you can start teaching right away."

"Oh my… I have never thought there would be option to teach calculus again! I think I forgot most of it but… yeah, I'll do it!" Daniel said and Anderson stood from his chair.

"Get yourself ready then! Your students will be waiting for lecture in the afternoon." Anderson said and left. Daniel was putting on his clothes and got himself ready to leave the hospital. In the meantime, Shepard and his squad landed on Tuchanka. Shepard escaped the shuttle as first, behind him Grunt and the last one was Legion.

"Grunt, I think it would be better if you lead us."

"Alright, Shepard. We will meet with Wrex so he says what we'll do next." Grunt said and led the way towards Wrex' hideout. As soon as they got there, Wrex recognized Shepard, but unfortunately didn't recognize Legion.

"Shepard! I cannot believe you actually… what is that thing doing here?!" Wrex pointed at Legion.

"It's ok, Wrex. He's with us." Shepard explained.

"Hmm, so the Geth works together with you, huh? Can you trust that machine?"

"If I may add something, I've been progressing on deep fusion with organics' quintessence." Legion explained and Wrex rubbed his head.

"Eeeeeh…"

"He has emotions, Wrex."

"Eh, emotions?" Wrex asked but shook his head, "No, I cannot bother myself with this. Shepard, follow me with your squad. I need to show you something, but you have to stay in safe distance…" Wrex gestured and all of them followed him towards a medical tent. They stopped once Shepard and others saw tens of krogans lying helplessly on the ground.

"Oh my god…" Shepard said in wonder to see many infected krogans.

"The disease has killed many of us already, Shepard. We don't know how to cure it, our medical officer died just few days ago. The situation is critical and we only send stronger krogans to the Citadel for good medical care. This is our extinction…"

"Grunt mentioned something about salarian scientist who brought this here."

"Hah, yeah. That salarian scum wanted to do some research here, probably about genophage. Before we noticed anything strange about him, he was starting to groan of pain, became languid, sweaty. First we thought he had some regular disease that wouldn't be infectious for krogans. I was wrong…"

"What happened?" Shepard asked.

"As in sign of kind behavior, I tried to help him. My medical officers tried to give him proper treatment. As you can guess, krogan medicine is in diapers. Besides that, something strange was happening. We never saw such aggressive disease. He was vomiting, dehydrating and soon he was bleeding from all cavities he had."

"What did you do with him?"

"We considered that we couldn't help him in our conditions so we spared him of his suffering… we incinerated him."

"That's a little… inhumane, Wrex. But I guess there was nothing else to do."

"Yeah, it didn't help. We thought our lives would return to the same point as they were before. However, most of my krogans were falling in fevers as well and many of them already died. When we looked inside their body, we saw the same result. Internal organs in one bloody pudding." Wrex laughed a little bit.

"How come you are still alright, Wrex?"

"I cannot predict whether I'll die today or tomorrow, Shepard. Maybe I am already infected but we don't know how long is the incubation period."

"Do you know something about the salarian?"

"Hmm, yeah. We asked him what was his occupation before. He said he was working on releasing cryogenically frozen test subjects on the Citadel."

"Well, this might be the reason, Wrex."

"You mean you knew about it, Shepard?"

"There is one human in my crew called Daniel. He was born in 1996 and since 2025 was frozen in his pod. He and other 9 subjects were transported on the Citadel. Possibly some of those humans were infected with the hemorrhagic fever. Daniel explained us that there was epidemic of this hemorrhagic fever back on Earth in those times. As I've searched more information, the mortality rate is about 90% and back then there were about 20 000 people dead."

"So your human knows this… what now? We need a cure! I cannot keep sending krogans to the Citadel. We have limited number of shuttles!"

"That's why we're here. We've got the cure."

"You do?"

"Yes… but limited supply. Just tell us how to apply it massively."

"There aren't many options. You can use the Shroud. A salarian construction which stabilizes our atmosphere here. It can be used to spread something as well but if I can tell something, it's dangerous route to get there."

"We'll do it somehow. Grunt, Legion, let's go!" Shepard said and they went to get in one of the heavy krogan range rovers. In the meantime, Daniel was at place and saw the students sitting at the auditorium. First, he thought he won't make it but then he remembered about his times on faculty and entered the room.

"Good day, students." Daniel said and took the position in front of the board, "Maybe you wonder why I'm here. Well, basically I was offered to explain something to you from calculus. I was informed that all of you are here learning calculus according to human educational system. You may like it or not, I hope you finally managed to get into it because I am supposed to tell you something about… improper integrals… yes?" Daniel asked the salarian student who held his arm up.

"We've heard that you were in cryo-stasis for 160 years… is that true?"

"Yes, pretty much. And because math is not changing somehow particularly, it's only good because I can do the lecture here for you with the knowledge I used to have 160 years ago!" Daniel smiled and students laughed, "No, I think something remained in my head so let's get started. Like I said, our topic is called the Improper integrals." Daniel said and started writing on the interactive board with stylus pen.

"So you all came through the basics of your first calculus course. You know what is a limit, derivative, integral, the surface under a curve, discontinuity of function and so on. Besides that, you should know how to use trigonometric substitution, the u-substitution, integration by parts, integration by partial fractions and many more these techniques. Now we will put everything together and we'll talk about improper integrals. So why are those integrals improper…" Daniel said and wrote example of integral with one bound at number, the other bound at positive infinity.

"So you are given this problem. You are supposed to find a surface under a curve from one number to infinity. Here comes the idea of improper integral. You may find it irrational to seek for a surface under a curve that goes to infinity, but let's think about it the other way. Replace your infinity with number, let's call it b. When you do so, you can rewrite your integral with b as the ending point but you have to tell yourself – If I know that b approaches infinity, what do I need to use to send b to the infinity?"

"The limit…" the turian student said and Daniel nodded.

"So we will go like this. You will replace infinity with b but you have to write limit in front of your integral. Now some more theory before I go further…" Daniel said and continued writing the cases of improper integral. The infinite interval, the infinite discontinuities and adding the one-sided limits to the solution.