No idea which episode yet, but EW says:
Burn Notice: John Seda (Homicide, The Pacific) will guest star on the USA smash later this season as Cole, a disgruntled ex-Marine who now works as a killer for hire. Elsewhere, Tim Matheson and Garret Dillahunt have signed on to reprise their respective roles as “Dead” Larry Sizemore and jailbird Simon.
Season four of Burn Notice kicked off last week. The show airs Thursdays at 9 on USA.