With Neo Metal Sonic far behind him, Sonic's due for some rest and relaxation, right? Wrong! With Doctor Eggman restored to his original self by Doctor Starline, there's a new threat facing the planet - an awful Metal Virus that infects everyone and everything and warps their mind into terrible Zombots - including Sonic himself!
Infection's a pretty bold storyline, especially after the first year built up to that epic conclusion. This one starts off a little slow, with two confrontations with Rough and Tumble before things really get moving, but there's definitely a sense of creeping dread in the earlier issues as Doctors Eggman and Starline begin testing the Metal Virus as a subplot before it becomes more of a problem in the final issue of the trade, ending on a cliffhanger that's going to lead right into volume 5.
The art is the continually rotating team that we've come to expect, with issues pencilled by Adam Bryce Thomas, Tracey Yardley, and Jack Lawrence. Sonic may not have a consistent art team, but the styles between the artists on rotation are pretty similar, so it's never too jarring. I think Sonic's world is pretty 'simple' in essence, which makes it easier to keep up the consistency.
Infection's the calm before the storm, most definitely, but it lays sufficient groundwork for what's likely going to a huge problem for Sonic and friends.