Acknowledging Loki's status as a Prince of Asgard seemed to be exactly the right approach from SHIELD. Even though Loki professed to dislike his home, he seemed to care about his position. Tony secretly thought that being reconciled with his family was something that would overjoy the demi-god, but he wasn't stupid enough to say it out loud.

There was only so much Loki was willing to admit, and since the demi-god knew stuff that was in his head just like Tony knew what was in Loki's, he figured it was better to keep his mouth shut. They both had each other in a corner when it came down to it and Tony didn't want his personal stuff spread around, so he kept his silence on Loki's.

Loki turned out to be intelligent, sarcastic and sassy when he wasn't trying to take over and Tony found himself liking Loki a lot as they got to know each other over the next two weeks. Even Clint seemed to settle down and accept Loki's presence once JARVIS had tracked down actual proof of Coulson's survival. They still didn't know where the man named Agent was and Tony was considering just confronting Fury, but the evidence was clear: Coulson was alive. Fury probably had a nefarious plan they could all wreck once JARVIS had tracked down more evidence.

It was just after Clint has changed his attitude they had had the coffee incident. It had taken Tony falling asleep in his workshop for anyone to realise all the coffee in the building had become decaf. It hadn't been switched with decaf, it had actually become decaf and Loki did the most beautiful innocent face Tony had ever seen. Luckily even Natasha found Tony snoring funny and JARVIS, the traitor, played it all back for everyone to see.

It had become common place to see Loki wandering from the microwave with a mug that was very definitely not filled with coffee first thing in the morning. No one mentioned blood, because it made Steve go a funny colour, but everyone knew what it was. Loki was staying on Thor's floor which had its own kitchen, but it had become kind of the thing for the team to have breakfast in the communal kitchen on the main floor (totally Steve's fault) and Loki had just slipped into that with them.

Bruce and Loki had bonded over tea; the God of Mischief was not a lover of coffee like his brother. Tony had decided to forgive Loki for that though, because he had a big crush on Loki's brain. Almost as big as the one he had on Bruce's and bigger than the boner he had for Loki's body, which was huge, in both cases.

Watching Loki steal Thor's pop tarts was also a daily joy. Steve insisted everyone eat properly in the mornings, but Thor always added on pop tarts and Loki seemed to have picked up a taste for them. The chocolate ones usually disappeared before Thor even got a look in, but Thor didn't seem to mind. It was cute how Thor always heated a chocolate one and a blueberry one first and then pretended not to notice when Loki stole the chocolate one right off his plate.

However, there was one thing Tony had noticed day after day: Loki didn't seem to consume the blood with much enthusiasm. For the last two days Loki had seemed irritable and tired and had spent more time curled up reading on Thor's floor than in the lab with Tony and Bruce. Since they had become science buddies, or rather, science and magic buddies, that was unusual.

He knew Loki used some kind of glamour to deal with the sensitivity to light issue, but as he watched Loki heat his usual mug of blood, Loki looked pale even with the magic.

"You feeling okay?" Tony asked as he mixed up his usual smoothie.

"I am fine," Loki snapped back.

"Hey, I was only asking."

Loki took a deep breath, still looking at the microwave, before turning.

"I am sorry," Loki said; "I am not feeling quite myself."

There was a ding from the microwave before Tony could ask Loki what the problem was, and the demi-god turned away again.

"Anything I can do?" Tony asked as Loki retrieved his mug.

"I believe I may have strained my magic," Loki replied, walking slowly over to the table. "It has been a long time since I have been able to relax. I am sure it will pass."

It never did to push Loki, so Tony accepted that and carried on preparing his breakfast. Thor and Steve appeared moments later, fresh from their morning shower after their jog around Central Park.

"Good morning, Brother, Tony," Thor greeted; "is it not a marvellous morning?"

"Not bad," Tony replied; "did you two make many maidens swoon with your manly muscles this morning?"

"Steve had to rescue a small canine from the jaws of a larger beast," Thor began and then joyfully regaled them with the full story while Steve started making breakfast and tried not to blush.

If there was one thing Asgardians knew how to do it was tell stories. At various points in the tale Natasha, Clint and Bruce arrived, which was a full house, because Pepper had been at work for a good hour already and Jane had come for a visit the previous week, but hadn't stayed more than a couple of days. Thor was very enthusiastic about Loki getting on with his girlfriend and eventually Jane and Loki seemed to bond out of sheer self-preservation.

Tony kept an eye on Loki throughout, but he couldn't see any difference from normal. Loki unenthusiastically drank his blood, stole a pop tart and accepted a cup of tea from Bruce. It was only when Loki was halfway through the pop tart that anything changed. Thor was explaining how Steve had tried to extricate himself from the grateful owner of the small dog when Loki put his half-eaten pop tart down and grimaced.

It could only have been a second later when Loki moved, not as fast as Tony had seen Loki move, but definitely fast, and ran to the sink, bending over it and being very loudly ill.

"Brother," Thor was out of his seat and at Loki's side a second later, "what ails you?"

Loki couldn't answer, because he was still vomiting, at which point Thor was a good brother and grabbed his hair out of the way for him. It was decidedly unpleasant, but also very clear that Loki simply could not stop. Tony wasn't good with such things and kept his distance until there was the sound of water running.

"Thor," Loki said very quietly as he slowly stood up, but whatever Loki was going to say was lost as the demi-god collapsed in a dead faint.

It wasn't much of a surprise when Thor scooped his brother up before Loki could hit the ground.

~*~

"Well?" Tony asked half an hour later when Loki was tucked up in bed with Steve keeping watch and everyone else was in the conference room for a powwow.

"If I didn't know better, I'd say he'd been poisoned," Bruce said.

"Who would do such a thing?" Thor boomed.

"Not SHIELD," Natasha said quickly; "not after they've given him diplomatic status."

"They couldn't have anyway," Tony added, "I switched out their blood on the second day, because Loki didn't seem to like it."

"Could it have been an accident?" Clint asked. "Just one batch this morning?"

Tony looked at Bruce.

"He's been different for a couple of days," Bruce revealed.

"I too have noticed he has not been himself for several days," Thor agreed, "but he assured me there was nothing about which to worry."

That didn't give them many alternatives.

"What about something else he ate?" Natasha suggested.

"It was definitely the blood," Tony replied; "he didn't steal the pop tart with his normal enthusiasm. He was going through the motions."

When Natasha did not argue he knew she had seen the same thing.

"Then what could it have been?" Clint asked.

"Maybe it's something he's not getting," Bruce suggested with a thoughtful crease between his eyebrows. "I've seen this kind of reaction with food intolerances where a person is missing an enzyme. It could be why it has taken this long to show."

"But he was definitely fine when he got here the second time," Tony said. "He was half dead when he bit me, but when he came back to say thanks he was buzzing."

"So maybe it's something to do with the blood being from a bag?" Bruce said. "Maybe the preservation process has added something or taken something away he needs."

That made more sense and Tony's mind began to rotate through all the possibilities.

"Holy crap," he said as he realised what was staring him in the face. "Thor, don't take this the wrong way, but was your brother a player back in Asgard?"

Thor frowned.

"I do not understand."

"Did he like the ladies, or the guys for that matter?" Tony clarified.

"Oh," Thor said, clearly not at all bothered by the question, "no, Loki was most particular in his dalliances and even more so with his affections. It was one of the things members of the court would often gossip about."

"Then I think it might be the sex," Tony said and looked at Bruce.

"What sex?" Clint asked, clearly confused.

"When he bit me, the first thing I felt was an incredible sexual overload," Tony explained. "I somehow pushed through it, but my body still responded. When he came back, he told me he'd been getting his blood by seducing people. Sex releases all sorts of things into the body; what if he needs something from that to properly digest his meals?"

"If his behaviour has changed that much it could be an instinctive adaptation," Bruce agreed.

It made sense and it was the first thing that had since Loki threw up in the sink. Tony still didn't want to think about that.

"I have samples of..."

"Don't say it," Tony interrupted Bruce and made a face; he really didn't want to think about that.

"I can run some tests," Bruce said. "Want to come help?"

It was hard; Tony was not good with bodily waste products, but it was so tempting. In the end science won out.