There were a few changes to the BAU team in season 6 of Criminal Minds,and many fans were not satisfied with the results.The team lost JJ and Prentiss,received a rookie,who did the best she could, and spent the end of the season grieving. Now the team together again in season 7.
When asked if fans should expect to see more Ian Doyle in season 7 Criminal Minds dvd, Paget Brewster said, "He's back, yeah. Everybody loves Timothy Murphy!" Even though you had to hate Doyle for what he was doing to Brewster's Emily Prentiss last season and what it led to, it did make for one of the strongest arcs on the show so far and featured amazing acting from both Brewster and Murphy. Murphy played Doyle perfectly, and Brewster shined as Prentiss hid what was going on from the others, and left them behind to protect them.
When Doyle was last seen, he had stabbed Prentiss, leaving her to die, and left to find his son whom he had thought was dead. JJ and Hotch were the only ones to know that Prentiss, in fact, did not die in "Lauren," and JJ set her up with bank accounts and passports in Europe. Prentiss had to leave her old identity behind to stay safe with Doyle still out there, and it's no surprise that Doyle's returning as the BAU works to get Prentiss back where she belongs.