It was already night time after a nice summer day in Brooklyn. As the other turtles were asleep, Master Splinter was either sleeping, meditating, or grieving the predicament that befell his daughter, Karai/Miwa. Since the incident, Donatello became an insomniac, constantly experimenting or researching the necessary components for Karai's/Miwa's retro mutagen. Even though Donnie is constantly in his lab, he sensed a massive change that befell upon the lair ever since that night.
Michelangelo is still in his happy-go-lucky personality and is doing any of his favorite hobbies (reading comics, skateboarding, feasting on pizza etc.). Strangely, Mikey stopped pulling pranks or clowning around with his older siblings. Same thing could be said about Raphael. He still hangs out with his friend Casey Jones and does vigilante-like business with him. Raphe silently became Casey's mentor and taught him numerous, yet effective fighting techniques. This training has formed the two into a solid duo. Strangely, amongst his brothers, Raphael has stopped his gruff and tough personality and has taken up meditation with Splinter. Yet when Donnie sees him, Raphe's new behavior grimly reminds him of a caged animal. Leonardo seems to be the one going into a deeper downward spiral than the other two. Even though he is occasionally seen practicing with the dummy, playing pinball, or watching the Captain Ryan show, Donnie knows that Leo is still blaming himself for not saving Karai/Miwa, and has also been meditating alongside Splinter as well. Sometimes Donnie understood Leo's feelings by looking upon Timothy, whom is now an oversized frozen canister.
Even Donnie admits that he is having a downward spiral of his own. Ever since he has been trying to develop the retro-mutagen, the work has left him isolated from the others and strained his friendship with April O'Neil. The last thing he heard about her was that she and Casey eventually became a couple. She sometimes comes down to the sewers and train with Splinter. Yet even through his isolation, Donnie believes that April has feelings for him.
While not making the retro-mutagen, Donnie seemed to benefit upon the scrounging of both Kraang and human technology. Lately, he has upgraded the Shellraiser drastically; adding more armor, another turret, and more defensive countermeasures. He also redesigned, upgraded and created another Stealth Bike, making them look more like motorbikes than the previous chopper model. Donnie upgraded Metalhead to be a completely independent robot. He also added in him some refined metal to silence its annoying clanking sounds and made a cloaking device. Since then it has been guarding the lair and sewers, which prompted Donnie to create a homing beacon on the lair so when Metalhead's patrol is over, it doesn't get lost by the massive maze of the sewers.
However, his new invention seems to trump everything he has made. After watching Mikey play a video game called "Arkham Origins", Donnie managed to create a similar gadget to Batman's "Detective Vision" by using a Kraang droid's visor along with human technology, like thermal and infrared cameras and many scanners. Setting it online was perhaps the most difficult thing ever. He needed about five to six different computer systems to hack both the NYPD's and National criminal databases, along with evidence found in all of their cases like gunpowder, human DNA, residues of chemicals, elements etc. Perhaps the most unique thing about "Detective Vision" is the ability to "play" crime scenes in the most accurate manner. Donnie had to scavenge many criminology books and video flash drives in order to get the most accurate possibilities of what happened in a crime scene.
However his ingenuity didn't stop there. Donnie managed to use the remaining bits of Kraang and human technology to create similar gadgets named "Tactical Vision" for combat effective purposes. Once ready, Donnie plans to give it as birthday presents to both Raphe and Leo.
Yet, Donnie is unaware of the discovery he will make upon his first usage of "Detective Vision".