It made a very nice change to move out of the lab a little, and work through the suspects in a slightly more old-fashioned whodunnit style. Not the most thrilling episode ever, but well paced for the subject matter.
The thing that concerns me is, episode by episode, Jo is becoming more and more of a Mary Sue. She knows everything, she's seen everything and she smugly imparts that knowledge to all the others, including Mac. Saint Jo is a little wearing. Every episode so far has included some special example of Jo's particular brand of cleverness.
I find it a bit odd that Mac not only seems to defer to her, he rather uncharacteristically appears to welcome her advances. This is not the cautious Mac that we are used to.