Disney XD’s Phineas and Ferb are getting Lost this fall, but at least we now know when to find them.

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The network on Friday announced that the animated series’ Lost-inspired episode — first revealed at Comic-Con — will air Monday, Sept. 29, at 7:30/6:30c.

From the mind of Lost co-creator Damon Lindelof, the episode finds Phineas and Ferb discovering a mysterious capsule in their backyard. Spoiler alert: opening said capsule leads to very bad things.

Lost star Terry O’Quinn is lending his voice to evil scientist Professor Mystery, while Jane Kaczmarek (Malcolm in the Middle) and Rob Morrow (Numb3rs) will play capsule passengers Denise and Bernie.