If you are looking for a musical "piece" (a cover song) played during an episode 4:
You might be thinking of a "piece" like Jaukeem Fortson’s cover of "Easy On Me" by Adele. [S5E4] On Me
You can find a detailed breakdown of the plot and character arcs on Wherever I Look . 2. The Boys (S5E4: "King of Hell") If you are looking for a musical "piece"
The episode " No Puedo Hacerlo " (S5E4) features a notable version of "The Scientist" by Coldplay (feat. Lindsey Stirling & Kina Grannis). [S5E4] On Me