Okay: we know it’s a game that takes place in the future; features narrative motifs of widespread panic and control; enables players to chart several paths within in a branching, mutable campaign; and for all intents and purposes fashions itself as a genuine shooter installment in one of gaming’s preeminent franchises… but Mass Effect 2 isn’t that similar to Call of Duty: Black Ops II, is it?

Someone along the Activision supply chain got fooled. Although almost surely a mishandling or manufacturing software glitch (though we’re not pretending to be experts here) several gamers who purchased the retail-disc PC version of Call of Duty: Black Ops II are indicating that its second disc — the one necessary to complete the installation process — actually contains information for Mass Effect 2, the 2010 sci-fi RPG actioner from BioWare and heated Activision rival Electronic Arts.

Retailers around the world conducted midnight launch events for Call of Duty: Black Ops II this Tuesday — Activision, naturally, predicts it will be counted as the largest entertainment release, revenue-wise, of all-time — but it wasn’t long before message boards like Reddit, 4chan, the Steam forums, and the official Black Ops II forums began reporting the identical predicament.

Some even filmed it. YouTube user zeroiez, in the video below, provided a NSFW reenactment of his experience inserting Black Ops II’s second disk — fresh out of the box at 1:45 AM and labeled with the game’s official logo — into the drive on his PC.

Fortunately, victims of of the mix-up can still play Black Ops II; each retail version of the game comes with an additional Steam download key, allowing the content to be installed digitally. The extra time will prolong the wait — for those who might have already endured a long midnight launch line, there might not be a worse feeling — but so far nothing indicates the keys are accidentally registered to Battlefield 3.

Call of Duty: Black Ops II is now available for PS3, Xbox 360, and PC. A Wii U version will be available as one of the console’s launch titles on November 18th.

Follow Brian on Twitter @Brian_Sipple.

Sources: Reddit, 4chan, Steam, official Black Ops II forums [via VG 24/7]