After debuting in the final scene of "School Reunion", K-9 Mark IV returned in spin-off series The Sarah Jane Adventures' premiere episode Invasion of the Bane, where due to licensing issues with creator Bob Baker it is explained that K-9 is sealing a black hole and can only communicate briefly and infrequently with Sarah Jane. The character makes an heroic appearance in the first series finale The Lost Boy, to do battle with rogue alien supercomputer Mr Smith (Alexander Armstrong), demonstrating new CGI teleportation and hovering features. K-9 Mark IV's interfaces include at least one USB port.Subsequently, the character appears briefly in the Doctor Who series four series finale "Journey's End" (2008), wherein K-9 and Mr Smith assist the Doctor in returning Earth to its proper position. K-9 next appears in the comedic Red Nose Day 2009Sarah Jane mini-episode "From Raxacoricofallapatorius with Love". A deal with the creators of K-9 having been struck, K-9 Mark IV became a regular character in Sarah Jane in third series story The Mad Woman in the Attic (2009) until the series four premiere The Nightmare Man (2010), where he accompanies departing series regular Luke (Tommy Knight) to university. He appears again in series four finale, Goodbye, Sarah Jane Smith. Though he doesn't appear in the serial, it is mentioned in The Man Who Never Was (2011) that Luke invented a special dog whistle to summon him with.