Working together (13)
(Another definition for collaborating that I've seen is " Jointly working".)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">working together</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for in tandem that I've seen before include "One behind the other or alongside" , "'One behind the other, as on a bicycle (2,6)'" , "Working together" , "Manned it as twosome" , "Together - as on a bicycle made for two" .)
(Another definition for as one that I've seen is " Totally united".)