Loki does not understand the plan.
He's not entirely convinced there is a plan.
There sure is something happening. He's watching it all go down from the Quinjet. He's just not entirely sure what this "something" is, and the Avengers can't seem to make up their minds about that, either.
So he just sits there, and he watches. He watches Steve jump off a bridge and onto a truck. He then watches Steve almost get blasted right off the truck. It takes all of his self-control not to step in, but he doesn't want to give himself away. Nobody can know he's here.
He follows Steve's fight from afar. He keeps a careful eye on them, watching as Steve dodges Ultron's attacks, blocks his blasts, throws his shield... and then loses it as Ultron tosses it aside. Loki bites his lip, looking back as the shield fades from view. He could get that. It would be so easy to just bring it to him. He could toss it right at him and move on like nothing ever happened.
But they'd know. They'd know something wasn't adding up, and they'd doubtlessly realize he was behind it. And it's ridiculous that that stops him. He shouldn't have to hide the fact that he wants to help. It makes this much harder than it should be.
Then he catches sight of Natasha speeding toward them on a motorcycle, and he feels himself relax a little. He's not the only one watching out for him. Steve has his whole team with him. He'll be okay.
Loki's attention is stolen when two drones attack the Quinjet. The only one on it is Clint, and with both Steve and Natasha fighting their own battles, Loki almost feels like this should be the least of his problems, but at the same time, there's nobody around that can help him. Steve and Natasha are both on the ground. They have each other's backs. Clint doesn't have that luxury.
Loki turns his attention away from them and to the Quinjet. He watches as it shoots straight up, trying to shake the drones off. When it doesn't work, Loki begins scheming. If he hits the drone on the bottom with his magic the right way, Clint shouldn't be able to see it. And maybe if he hits the one on the top...
But Clint does a few rolls in the air, and finally, he manages to shake the drones off. Loki watches just long enough to make sure he's safe, then searches for Steve again. He's on a train now, but he's still fighting Ultron, a one-on-one he has no chance of winning. He's holding his own at first, blocking every hit sign his shield, until he doesn't, until Ultron slams him in the leg and nearly sends him to the ground.
Loki glances around nervously. At what point is he supposed to step in? Does he wait? Does he really have to hold off until Steve is seconds from death before he gets involved? Maybe he can step in now. It's just Steve. He doesn't expect the same backlash from Steve that he'd get from everyone else. As long as he's helping, Steve won't care. He might even be relieved to have an extra hand.
Just before he can make up his mind, somebody else steps in, and steps in fast. The train seems to blur before his eyes, and then he's there, that boy from the factory – Pietro, he's come to learn – seemingly from nowhere, body-slamming Ultron out of the way. Then the bars of the train bend themselves in a cloud of red, blocking his path, and there stands the girl from earlier, the Maximoff girl, Wanda.
Ultron seems disappointed, apprehensive, when he sees them. "Please," he says quietly, "don't do this."
"What choice do we have?" the girl counters.
That seems to be all the persuasion Ultron needs that these kids aren't his friends, because he shoots a blast toward the boy, who just barely dodges in time. He blows a hole through the front of the train, then another through the side, and he flies off through it.

BINABASA MO ANG
Loki Misses the Asgardian Prison System
FanfictionThe Allfather has run out of options. Loki has made a fool of him and a fool of his realm one too many times. If he won't stay in his prison on Asgard, maybe he'll fare better stuck in Stark Tower. (Needless to say, Tony doesn't like that idea. He c...