A quick look at the previous volume, D.Gray-man, Vol. 15:

Lulu Bell from the Noah Clan has entered the Black Order's headquarters to retrieve the Millennium Earl's precious Egg.  With several of the Order's Exorcist without weapons or in bad shape, Allen and Bookman will have to fight off the massive amounts of Akuma, and protect the Egg, until more help comes.  Things get worse however, a level Four Akuma has entered the ring.  This is the first time ANY of the Black Order has seen a level Four.  Now Allen has to fight not only the regular Akuma, but an unknown level Four too.

In volume 16, Lenalee has escaped from the medical ward with Lavi.  They are headed to Hevlaska, the guardian of the Innocence.   Lenalee has agreed to have Innocence implanted into her body, a forbidden practice with unpredictable consequences.  The level Four Akuma has been able to defeat Allen and is now headed for Hevlaska.  Will Lenalee be able to host Innocence again?  Or will the level Four make it to Hevlaska before the Innocence can ever be implanted?

Highlights

I was really worried about this volume.  The previous volume didn't have much promise for the series, and I felt that it was going to be difficult for this volume to get it back to standard.  I was surprised, however.  The story was back to progressing, and the feeling of being trapped with absolutely no way out I got from vol. 15 was cleared in vol. 16.  The way the battle against the level Four came to a conclusion was one of my most favorite yet.  It was done in a way that is pleasant to the reader, and not the usual "I'm gonna beat you, 'cause of my dream" ending I see a lot.  I was also really happy with the aftereffect of the battle.  The Order is moving to a new location.  Everyone is back to their good old selves, bringing back the comedy.  

Overall

This volume has done an excellent job of redeeming the series from the previous volume.  It was an easy and fun read.  I give it thumbs up.  But, there is one problem with this volume that get a thumbs down, a new mini-arc.  D.Gray-man is full of mini-arcs that, in time, will take up a whole volume, and they don't tend to progress the plot at all.  Well, in Vol. 16, Komui (the director of the Black Order Headquarters) has one of his failed experiments which starts an epidemic in the current Headquarters.  It's a virus that causes people to turn into zombies.  So now Allen and some of the other main characters have to turn everyone back.  I found it to be rather pointless to the plot, especially, right after a major battle.  On top of that, it's going to be carried into the next volume. I hope it gets back to the central arc soon.

Overall, I'm pleased at how the series picked back up, and I'm interested in what new enemies they will encounter.  I'm also curious about the new Headquarters, which was hinted to be in England.  Now all that needs to be done is the mini-arc's resolution, and the moving of the Order to the new location, and it should be back to the plot.  I'll be waiting for the next volume.

ComicsOnline gives D.Gray-man Volume 16, Blood and Chains, 3.5 out of 5 Bazaar Experimental Concoctions that Appear to Achieve Nothing.