In the third season, Donald reveals that he and Douglas weren't the only kids in the family. They had an older genius brother named Daniel (nicknamed Danny just like Donald and Douglas were nicknamed Donny and Dougy) who currently resides in Hawaii! When Daniel calls one day to ask about him, Donald tells him that Douglas is alive and about his evil ways. He believes him since they both knew how michevious he was as a kid. Learning about Douglas's evil ways, he sends them his only son, Derek, via transporter, so that Donald could upgrade him to become the ultimate 14-year-old bionic machine! Now, together, Adam, Bree, Chase, and Leo must help their new leader master his powers... but worst of all, he must master his glitches too, so that he can become the Lab Rat's "secret weapon"! But elsewhere, Douglas is more powerful then ever since he has reprogrammed Marcus (after the accident) to become bionic, and not an android. However, Marcus does not have new powers and only his old ones. But when Douglas finds out about Derek, he upgrades (or sholud I say "steals, and then upgrades!") his own "secret weapon", one that could be more powerful and experienced than Derek himself!
Dylan Everett as Derek Davenport
TBA as Josh
Stefanie Scott as Sarah
Will Forte as Daniel Davenport
Zendaya as Natalie Davenport/Natalie Beige
Flame as Dylan Everett
1. The Secret Weapon: Part 1 - In the first part of the Season 3 premiere, Donald reveals to the kids that he and Douglas have an older brother named Daniel (nicknamed Danny just like Donald and Douglas are nicknamed Donny and Dougy), who is currently in Hawaii! One day, Daniel calls Donald to ask how he is. But when Donald tells Daniel that Douglas is living and that he's out to get him, Daniel believes him since they both knew how michevious and evil he was as a kid. To help, Daniel sends Donald his only son, Derek, to him via transporter, so that Donald can upgrade him and make him their "secret weapon"! Now, the Lab Rats, Leo, and Tasha must make sure that everything in the house is fine while Donald is upgrading the 14-year-old. Now they must be ready, for everyone is about to meet possibly the most powerful, yet childish kid in their life!
- This is the first episode in which Dylan Everett and Angel Parker are in the main cast.
- Will Forte, who plays Eddy, is also Daniel in the episode. It is revealed in the episode that Eddy was created by both Daniel and Donald, side-by-side, and they gave Eddy Daniel's voice.
- Before Season 3, Eddy had returned since Chase hacked into Douglas's computer to return Eddy's software to the house
2. The Secret Weapon: Part 2 - In the second and final part of the Season 3 premiere, the Davenport family meets Derek, the kids' cousin who has been upgraded into their bionic "secret weapon" to defeat Douglas once and for all! Sent by Donald's older brother, Daniel, they must help Derek fit in and master his powers... and glitches! When they first take him to school, Derek's new powers and childish personality gets the best of him and he uses his kinetic abilities in secret, but accidently breaks the generator, shuting down all electricity, including the lights. Due to this, Derek's glitch (Scotophobia Extreme) kicks in causing him to break everything in his way due to his fear of the dark (scotophobia). Now the Lab Rats, and Leo must work together to use their new leader's new powers to fix the generator!
3. Raining Cats and Dogs - To impress Owen, Bree gets two kittens and a puppy to show Owen that she cares for everything and everyone. But her plan backfires when Derek starts glitching severely. When they call Daniel he tells them that Derek has a severe allergy to cats and dogs and if he gets too close to the pets, he would need an EpiPen. Leo and Donald then tell Bree to either choose between Owen, or Derek, because there can only be one choice. Meanwhile, Chase gets a cold because Adam had "accidently" launched him into the freezing rain. Now, Adam must be Chase's servant until he stops Sonic Sneezing (Snot Cannon). The only cure could be Tasha's horrible-tasting soup, which Chase refuses to drink.