Bad Heroin?

Dead bodies all over:

• Three men were found dead in a South Loop apartment Monday morning, and police believe their deaths were drug-related.
  
  Police and ambulances were called around 11:40 a.m. to 633 S. Plymouth Ct., where they found the three men dead in an apartment, said Chicago Police [...].
  
  Drugs and drug paraphernalia were found in the apartment, he said.

Once again, could someone describe "good heroin" to us? This is the second mass overdose in a few days, but the first resulting in deaths - are we seeing a return of the fentanyl mixture that reduced the junkie population by dozens a few years ago?