digraph G {

    { // Define the actor nodes in the top

        // Make sure they're on the same row
        rank=same;

        // Style the actor nodes
        node [shape=box];

        actor1_top [label="Actor 1"];
        actor2_top [label="Actor 2"];
        actor3_top [label="Actor 3"];

        // Tie them together in the right order
        edge [style = invis];
        actor1_top -> actor2_top -> actor3_top;
    }

    // Define the actor nodes in the bottom. This is a copy paste
    //of the top subgraph -  s/top/bottom/g
    {
        rank=same;
        node [shape=box];

        actor1_bottom [label="Actor 1"];
        actor2_bottom [label="Actor 2"];
        actor3_bottom [label="Actor 3"];

        edge [style = invis];
        actor1_bottom -> actor2_bottom -> actor3_bottom;
    }

    // Style the event nodes
    node [shape=point];
    edge [arrowhead=none];

    // Define the event nodes. Here they are prefixed with
    // the actor name.
    actor1_event1
    actor1_event3

    // Now we connect each of the events like pearls on a string.
    actor1_top ->
    actor1_event1 ->
    actor1_event3 ->
    actor1_bottom;

    // Repeat. The event above has a corresponding node in the
    // destination actor.
    actor2_event1
    actor2_event2

    actor2_top ->
    actor2_event1 ->
    actor2_event2 ->
    actor2_bottom;

    // And one more time.
    actor3_event2
    actor3_event3

    actor3_top ->
    actor3_event2 ->
    actor3_event3 ->
    actor3_bottom;

    // We connect each event src/dest. First we make sure they
    // are vertically aligned.
    {rank=same; actor1_event1 actor2_event1}
    {rank=same; actor2_event2 actor3_event2}
    {ranke=same; actor3_event3 actor1_event3}

    // Finally, we connect the dots.
    edge [constraint=false, arrowhead=normal];

    actor1_event1 -> actor2_event1 [xlabel="start"];
    actor2_event2 -> actor3_event2 [xlabel="do something"];
    actor3_event3 -> actor1_event3 [xlabel="return"];

    // We use xlabel, as normal labels will skew the whole thing.
}