A Ukrainian Army element is escorting a press pool through a Ukraine/Crimea border area and comes across a pro-Russian militia element that has drifted across the border for some unknown reason.

The expected standoff escalates to a firefight, leaving seven militiamen dead and two Ukrainian soldiers wounded. The militia force falls back into Crimea and Ukrainian forces pursue.

A Russian SOF element hears the dustup and vectors to the area. The militiamen make visual and radio contact with the element, and break contact past its hasty position. The SOF unit suppresses the Ukrainian pursuit force, killing several.

In thr confusion, Ukrainian Army sources start reporting that a Russian unit has breached the border to attack a lightly-armed security unit. The entirety of Ukrainian military forces mobilize, with several formations making for the border at breakneck speed.

Russian forces move from high alert and begin occupying key terrain on the border. Cross-border firefights begin to flare up and a rifle company is lifted by heliborne means across the border to seize a road tunnel on the Ukrainian side, thereby cutting off that avenue of approach.

NATO shifts to emergency sessions and places forces on alert, but a consensus on a response is mired in uncertainty and worry. The US places various fighter and bomber squadrons on alert.

President Obama condems the outbreak of fighting and pledges that America will stand with Ukraine against "this blatant aggression."

Five minutes later, Putin addresses Russian TV, looks squarely into the camera and states that friends of Ukraine can only be enemies of Russia.

What happens across the next 24-96 hours?

How does it end?