The BAU heads to Philadelphia, Pennsylvania where the Replicator, the unsub who has carried out a series of crimes replicating cases recently solved by the BAU, has murdered his latest victim. The reason why this Philadelphia murder attracts their attention is that unlike the previous three murders by the Replicator, this one took place in a city other than that of the original crimes. Garcia discovers that the flowers sent by the Replicator to JJ were purchased through a credit card whose owner lives in Philadelphia. And Strauss gets involved as she feels this case undermines the work of the team. By the time they arrive in Philadelphia, what they find that is also unique is that a second murder has taken place in Philadelphia using the same MO, which the Replicator has not yet done. Tracking down the Replicator is made all the more difficult by an uncooperative Detective Rizzo, the lead police investigator who does not like the BAU's involvement. The Philadelphia victims all being nurses and the geographical location leads the team to closed case they worked on fifteen years ago. They believe they are close to catching the Replicator until... Meanwhile, Blake and Strauss try to deal with their past antagonistic relationship in different ways.