  We consider antiparallel Wilson lines in N=4 super Yang-Mills in the presence
of a codimension-1 defect. We compute the Wilson lines' expectation value both
at weak coupling, in the gauge theory, and at strong coupling, by finding the
string configurations which are dual to this operator. These configurations
display a Gross-Ooguri transition between a connected, U-shaped string phase
and a phase in which the string breaks into two disconnected surfaces. We
analyze in detail the critical configurations separating the two phases and
compare the string result with the gauge theory one in a certain double scaling
limit.
