Ep 1. Sink or Swim

In season 4 episode 1 of Lab Rats titled "Sink or Swim," the bionic trio – Chase, Adam, and Bree – are back to taking on more superhuman tasks at the Davenport Industries. The episode kicks off with the three siblings trying out an untested bionic upgrade that Professor Davenport had created. This upgrade is supposed to regulate their powers and prevent any accidental side-effects that may occur. But as they soon find out, things aren't as foolproof as they had hoped.

When they try to use their powers on their latest mission, they realize that their bionic abilities have gone haywire, causing some unexpected consequences. The siblings quickly realize how dangerous this situation could be, so they call on Leo for help. Leo, however, has his own problems to deal with as he's been tasked with finding a gift for Tasha's birthday.

Meanwhile, Douglas, the former villain who has now reformed, is seen talking to Chase, expressing his concern about the potential danger that the bionic siblings could cause. He urges Chase to use his intelligence to figure out a solution before it's too late. At the same time, a new character named Krane is introduced, who has some dark plans for the Lab Rats.

As the Lab Rats struggle to regain control of their powers, they are also dealing with an unexpected visitor – a girl named Reese who claims to have the same abilities as they do. However, the siblings quickly realize that Reese isn't who she appears to be when she tries to use them for her own gain.

As the episode progresses, the Lab Rats must face off against Krane who is revealed to be a former colleague of Professor Davenport's. Krane is obsessed with gaining control of the bionic technology and will stop at nothing to get what he wants. The Lab Rats must work together to protect their family and stop Krane from using their powers for evil.

The episode ends on a cliffhanger, leaving viewers excited to see what's in store for the rest of the season. Will the Lab Rats be able to defeat Krane and keep their powers in check? Only time will tell.

Overall, season 4's premiere episode of Lab Rats delivers on the show's promise of action-packed adventures and clever humor. The addition of new characters and the impending threat of Krane's plans add a new layer of excitement to the show that fans will surely enjoy.