You are absolutely not wanting to be here, at this blog, at the moment, considering what has just gone down in Boston. As of right now, all I know is that a pair of explosions went off at around the finish line of the Boston Marathon, with runners on course. (It came at about the 4:09 mark of the race, well after the top finishers had crossed the line.) People have been hit, people have been injured, and really it's your usual post-incident muddle of chaotic reports right now and it'll be a little while before we find out what exactly happened.
I'm just going to chuck you to someone able to give you better updates, namely a livestream of NBC News in Boston.