diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index 4fded61b..1df17c0e 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -442,6 +442,12 @@ if(USE_GLEW)
   target_link_libraries(twowindows GLEW::GLEW)
 endif()
 
+add_executable(twowindows_mutex twowindows_mutex.cpp)
+target_link_libraries(twowindows_mutex OpenGL::GL glfw Freetype::Freetype)
+if(USE_GLEW)
+  target_link_libraries(twowindows_mutex GLEW::GLEW)
+endif()
+
 add_executable(threewindows threewindows.cpp)
 target_link_libraries(threewindows OpenGL::GL glfw Freetype::Freetype)
 if(USE_GLEW)
diff --git a/examples/twowindows_mutex.cpp b/examples/twowindows_mutex.cpp
new file mode 100644
index 00000000..84b96a82
--- /dev/null
+++ b/examples/twowindows_mutex.cpp
@@ -0,0 +1,112 @@
+/*
+ * The twowindows example, but at least compiling and running the mutex locking code in
+ * morph::Visual.
+ */
+#include <morph/Visual.h>
+#include <morph/ColourMap.h>
+#include <morph/QuiverVisual.h>
+#include <morph/GraphVisual.h>
+#include <morph/vec.h>
+#include <morph/vvec.h>
+#include <iostream>
+#include <array>
+#include <stdexcept>
+#include <string>
+
+int main()
+{
+    int rtn = -1;
+
+    // Demonstrates use of offset (left at 0,0,0), lengths (3,2,1) and the 'thickness'
+    // scaling factor (0.5) for the coordinate arrows. Defines, and makes current a new
+    // window and OpenGL context.
+    morph::Visual v(1024, 768, "Window 1", {0.8,-0.8}, {.1,.05,.05}, 3.0f, 0.01f);
+    v.showCoordArrows = true;
+    v.showTitle = true;
+    v.backgroundWhite();
+    v.lightingEffects();
+
+    // If I define a second Visual here, then the OpenGL context will now be 'pointing'
+    // at this Visual v2
+    morph::Visual v2(768, 768, "Graph on Window 2", {0.8,-0.8}, {.05,.05,.1}, 2.0f, 0.01f);
+    v2.showCoordArrows = true;
+    v2.showTitle = true;
+    v2.backgroundWhite();
+    v2.lightingEffects();
+
+    try {
+        // Set up data for the first Visual
+        morph::vec<float, 3> offset = { 0.0, 0.0, 0.0 };
+
+        std::vector<morph::vec<float, 3>> coords(20*20);
+        std::vector<morph::vec<float, 3>> quivs(20*20);
+        morph::vvec<float> qlens(20*20, 0.0f);
+
+        size_t k = 0;
+        for (int i = -10; i < 10; ++i) {
+            for (int j = -10; j < 10; ++j) {
+                float x = 0.1*i;
+                float y = 0.1*j;
+                // z is some function of x, y
+                float z = x * std::exp(-(x*x) - (y*y));
+                coords[k] = {x, y, z};
+                k++;
+            }
+        }
+
+        k = 0;
+        for (int i = -10; i < 10; ++i) {
+            for (int j = -10; j < 10; ++j) {
+                if (i > -10 && i < 10 && j > -10 && j < 10) {
+                    morph::vec<float> r = coords[k] - coords[k-20];
+                    morph::vec<float> g = coords[k] - coords[k-1];
+                    // Compute normal and modulate by the distance from the centre
+                    quivs[k] = r.cross(g);
+                    if (coords[k].length() != 0.0f) { quivs[k] *= 1.0f / (1.2f + coords[k].length()); }
+                    qlens[k] = quivs[k].length();
+                } else {
+                    quivs[k] = {0.0f, 0.0f, 0.0f};
+                }
+                k++;
+            }
+        }
+
+        auto qvp = std::make_unique<morph::QuiverVisual<float>>(&coords, offset, &quivs, morph::ColourMapType::Jet);
+        v.bindmodel (qvp);
+        qvp->quiver_length_gain = 1.0f; // Scale the length of the quivers on screen
+        qvp->colourScale.compute_scaling(0, qlens.max());
+        qvp->quiver_thickness_gain = 0.02f; // Scale thickness of the quivers
+        qvp->finalize();
+        v.addVisualModel (qvp);
+
+        // Set up v2 with a graph, switching to the Visual v2's context first:
+        auto gv = std::make_unique<morph::GraphVisual<float>> (morph::vec<float>({0,0,0}));
+        v2.bindmodel (gv);
+        morph::vvec<float> x =  {-.5, -.4, -.3, -.2, -.1, 0, .1, .2, .3, .4, .5, .6, .7, .8};
+        morph::vvec<float> y = x.pow(3);
+        gv->setdata (x, y);
+        gv->finalize();
+        v2.addVisualModel (gv);
+
+        bool gotlock = false;
+        while (v.readyToFinish == false && v2.readyToFinish == false) {
+            v.waitevents (0.018);
+            gotlock = v.tryLockContext();
+            if (!gotlock) {
+                v.lockContext();
+            }
+            v.render();
+            v.unlockContext();
+
+            v2.lockContext();
+            v2.render();
+            v2.unlockContext();
+        }
+
+    } catch (const std::exception& e) {
+        std::cerr << "Caught exception: " << e.what() << std::endl;
+        rtn = -1;
+    }
+
+    return rtn;
+}