Despite the assumption of rest of his clan, Uchiha Shisui was neither stupid nor reckless. No one reached the rank of jonin with those characteristics, especially at the age of 14. However, at that moment, he was having doubts about his intelligence as h dodged another fireball from the giant caterpillar that had decided that Shisui would taste great as a roasted snack.

Even though he had been warned countless times by his superiors that the deeper sections of Forest of Death were only supposed to be used for ANBU team survival training, Shisui had entered the training ground without any backup.

It wasn't like he was unaware of the danger or overconfident in his abilities. But with the recent escalating tensions between the village and the Uchiha clan and the increasing probability of him using brainwashing genjutsu against his own relatives, he had just had enough. The revelation that Itachi had been spying on the clan didn't help the matter. For some time he just want to get away from everything- the village, the clan, Itachi, his teammates. With that mentality, Training ground 44 seemed like a good option.

12 giant crickets, 7 acid spitting leopards and 6 pyromaniac caterpillars later, breathing heavily with more scrapes, burns and bruises than he cared to count, he was regretting the decision of his past self. He was just about to hightail out of the forest (to never return again) ,when he flt a chakra flare in the pattern of a very old Konoha code (taught to him by Grandpa Kagami).

Despite his suspicions about infiltrators, Shisui proceeded towards the origin of the signal. Even if it was an enemy shinobi, it was necessary to detain him rather than leave him there with direct access to the village if he managed to get past the killer forest.

In a clearing not too far from Shisui's original location, he spotted a shinobi with his face down on the ground. He had spiky hair akin to Hatake-senpai and was sporting various injuries, which looked like they were from ninja weapons rather than any beast of the forest. As Shisui approached the shinobi rolled over to reveal a face Shisui couldn't help but recognize, before losing consciousness. It was a face he saw almost daily on the Hokage mountain.

Shisui was not prepared for this. The Second Hokage (Shisui activated his Mangekyou Sharingan just to be sure) was unconscious in the Forest of Death with life threatening injuries, while he should dead and buried long before Shisui was born. Oh my God, were those intestines that were poking out...

All right ,Shisui, calm down. Just treat it like a mission.

There is an unconscious shinobi with fatal injuries and suspicious background in a restricted section of the village.

Take him to the emergency rooms in ANBU headquarters.

Are those injuries going to be aggravated when he is moved?

Yes.

Is the shinobi going to survive long enough for interrogation if he is not moved?

No.

It took Shisui 2 seconds to come to a decision, following which he carefully picked up the Niidaime (Or a really good impersonator), and shunshined to the ANBU HQ.