The appearance of Matt Lauria probably won't make too big of a dent (I believe he'll show up in more episodes), but his character Ethan is somewhat interesting and relatable to Michael. He begins the episode hot-headed and ready to seriously hurt the guy who hurt his sister, but soon enough, he gets in to spy mode and is ready to say or do anything to get the job done.
The conspiracy grows larger as Michael recovers the tape of a convenience store where the incriminating phone was bought and finds that the person who bought the phone looks suspiciously like him. Along with the arrival of the CIA investigator Pearce (who's fashions herself as a bull dog), Michael has a lot to handle, but for now he can continue to suppress all information from the CIA.
"Square One" didn't have anything that stuck out to me--like most episodes this season--but it had its moments and the spy plot moved forward significantly. Whether these new elements introduced in the episode will have any effect is a question that will be answered later, however.