Manipulate[LocatorPane[Dynamic@pts,
pts1 = Take[pts, 4];
tempPts2 = Take[pts, -4];
pts2 = {tempPts2[[2]], 2 tempPts2[[2]] - tempPts2[[1]], tempPts2[[3]], tempPts2[[4]]};
allpts = Join[pts1, pts2];Dynamic@Graphics[{Green, Line[allpts], Red,PointSize[Large], Point[allpts],Blue,BezierCurve[pts1], BezierCurve[pts2]},PlotRange->{{-3,3},{-2,2}}, PlotLabel ->"Two Bézier Curves with Smooth Join"]],{{pts,{{-2.5,-1},{-1.5,1.5},{-1,1.5},{0,0}, {1.5,1}, {2.5, -1}}}, ControlType -> None}, SaveDefinitions -> True]