Where can I watch “Lab Rats” Season 4 Episode 21 online?

This page provides episode info and a legal-only guide. It does not host streams or downloads. Check official platforms and licensed services for availability in your region (US first).

Do I need to watch earlier episodes before “And Then There Were Four”?

Watching earlier episodes in season 4 helps you follow the plot and character arcs leading into this episode.

Watch Lab Rats Season 4 Episode 21 Online

“And Then There Were Four” — Watch "Lab Rats" Season 4 Episode 21 online in HD for free. Check streaming providers, cast, and episode details.

Jan 13, 2016 Season 4 Episode 21 22 min TV-Y7

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Lab Rats Season 4

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Season 4 Episode 21 — Aired on Jan 13, 2016 • runs about 22 minutes.

Notable cast/guest names in this episode include William Brent, Spencer Boldman, Kelli Berglund, Tyrel Jackson Williams.

This page includes 1 official still(s) (when available) plus legal availability links.

Looking for “watch Lab Rats Season 4 Episode 21 online”? This is a legal-only guide with synopsis, stills, and navigation for this season.

Synopsis

Everyone is shocked when Douglas introduces a fourth bionic sibling named Daniel who’s been living a normal life with an adopted family. Daniel later comes to the academy to meet his father, uncle, and cousins. After Daniel's bionics are accidentally activated by the Lab Rats, Donald and Douglas find out what happened they have to come clean to Daniel about his power-replicating abilities. Daniel also finds out that his cousins are actually his biologic siblings. Filled with anger, Daniel goes out for air on the beach, where Leo and him have a conversation about Douglas. Not too long after, Daniel, using Leo's abilities, accidentally causes a leak in the hydro-loop's fuel tank. After Adam and Daniel combined their powers to stop it, Douglas apologizes to Daniel for lying and Daniel decides to give Douglas a second chance.