Its an expression used when those at war with each other yet share a common threat. Setting aside their differences or conflict and joining together to stop a mutual adversary.
Although it may look like the present with Walter still driving his beaver panel station wagon, but the cheesy hair styles and terrible clothing all point to the 80's. Fringe gets to recycle their vintage version of an opening title sequence from last season in this week's flash back episode, "Subject 13".
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