The previous episode was a miracle of revival for the show, with a tight script, a detailed mystery, peopled with multiple eccentric characters. Harkening back to the original few seasons. This one is just plodding, mostly involving people describing their invovement surrounding a murder.
For example, instead of resorting to a lack of imagination in simply showing one suspect interview after another in a small detective room, a more imaginative script writer and director might have shown the details of the eventual crime from the moment the rock show began up to the murder. Then at critical times, one or more of the detectives stops the action and literally pulls a character out of the scene to interview him or her, then puts the person back into the scene. This concept continues until by the end of you learn who murdered the singer. In other words it's important to create an artistic conceit that moves the action along in a typical detective story you've seen lots of times before.