User Sizzor19 took to the Game Of Thrones forum yesterday to post a screenshot from the episode, which possibly proves that the White Walkers' decision to surround Jon Snow (Kit Harington) and company on that rock was all part of a deliberate trap to lure Daenerys (Emilia Clarke) and her dragons right to the Night King so he could kill them. I mean, why else would the frozen army have brought exactly three spears to battle?
While five White Walkers stood watch over the siege, three of them came armed with spears (the remaining two had swords). Three spears for three dragons, and Jon Snow was the bait. They knew that, if they waited long enough, Daenerys and the dragons would come to the rescue.
Plus, there's the fact that the White Walkers would have been able to kill the gang easily. Jon Snow was outnumbered and at the mercy of the elements. There wasn't much on his side that would have helped him if the wights started to attack — other than those dragons. By luring them over, the Night King has perhaps finally achieved a crucial part of his plan. We already know that, for some reason, they had those chains at the ready, so even if they didn't know when they'd be pulling a dragon out of the depths of a lake, they clearly knew that one day they would.
If this really was all part of the Night King's grand plan, I shudder (literally) to think what else he has up his icy sleeve.