After months of keeping all the rumors under wraps, "Big Brother" is officially locked in for a new season. CBS's long-running reality show announced on Wednesday that the theme for season 27 will be "Big Brother: A Summer of Mystery." In just a few days, houseguests will move into "Hotel Mystère" aka the "Big Brother" house decked out in skeleton keys, giant chess pieces, hidden passageways and a general mysterious vibe. And as Julie Chen-Moonves always says — we can expect the unexpected. However, the longtime host did reveal that season 27 will feature "a masked visitor, a secret accomplice and the shocking arrival of a 'Mystery Houseguest.'" Big Brother premiere date The "Big Brother" 27 mystery begins with a 90-minute premiere on Thursday, July 10, from 8 -9:30 p.m. It will be followed by another 90-minute episode on Sunday, July 13, from 8-9:30 p.m. before jumping into the regular summer schedule. What days will Big Brother air? After the premiere, "Big Brother" will air on: Wednesdays 8-9:30 p.m. ET Thursdays 8-9 p.m. ET (Live evictions) Sundays 8-9 p.m. ET This summer, "Big Brother" will air the most original hours of programming since the show first started in 2000 — with extended 90-minute episodes every Wednesday and the launch of "Big Brother: Unlocked" on Friday nights. Big Brother 27 house Some "Hotel Mystère" highlights include: A wall of keys, some with clues that might play into the game A sleeper car room "straight out of a murder mystery novel" that will have the first bunk beds the BB house has seen since season one A secret "wine cellar" (no actual wine included) The Venom Lounge and Poison Bar (again, no actual poison included) A boxing gym with a full boxing ring, heavy bag and workout gear