diff --git a/Stop.cs b/Stop.cs
new file mode 100644
index 0000000..9076ba0
--- /dev/null
+++ b/Stop.cs
@@ -0,0 +1,47 @@
+using System;
+
+namespace AggregateConsistencyBoundary
+{
+    public abstract class Stop
+    {
+        public int StopId { get; set; }
+        public StopStatus Status { get; set; }
+        public int Sequence { get; set; }
+
+        public void Arrive()
+        {
+            if (Status != StopStatus.InTransit)
+            {
+                throw new InvalidOperationException("Stop has already arrived.");
+            }
+
+            Status = StopStatus.Arrived;
+        }
+
+        public void Depart()
+        {
+            if (Status == StopStatus.Departed)
+            {
+                throw new InvalidOperationException("Stop has already departed.");
+            }
+
+            if (Status == StopStatus.InTransit)
+            {
+                throw new InvalidOperationException("Stop hasn't arrived yet.");
+            }
+
+            Status = StopStatus.Departed;
+        }
+    }
+
+    public class PickupStop : Stop { }
+
+    public class DeliveryStop : Stop { }
+
+    public enum StopStatus
+    {
+        InTransit,
+        Arrived,
+        Departed
+    }
+}
\ No newline at end of file

diff --git a/Stop.cs b/Stop.cs
new file mode 100644
index 0000000..9076ba0
--- /dev/null
+++ b/Stop.cs
@@ -0,0 +1,47 @@
+using System;
+
+namespace AggregateConsistencyBoundary
+{
+    public abstract class Stop
+    {
+        public int StopId { get; set; }
+        public StopStatus Status { get; set; }
+        public int Sequence { get; set; }
+
+        public void Arrive()
+        {
+            if (Status != StopStatus.InTransit)
+            {
+                throw new InvalidOperationException("Stop has already arrived.");
+            }
+
+            Status = StopStatus.Arrived;
+        }
+
+        public void Depart()
+        {
+            if (Status == StopStatus.Departed)
+            {
+                throw new InvalidOperationException("Stop has already departed.");
+            }
+
+            if (Status == StopStatus.InTransit)
+            {
+                throw new InvalidOperationException("Stop hasn't arrived yet.");
+            }
+
+            Status = StopStatus.Departed;
+        }
+    }
+
+    public class PickupStop : Stop { }
+
+    public class DeliveryStop : Stop { }
+
+    public enum StopStatus
+    {
+        InTransit,
+        Arrived,
+        Departed
+    }
+}
\ No newline at end of file
diff --git a/Tests.cs b/Tests.cs
new file mode 100644
index 0000000..f577ace
--- /dev/null
+++ b/Tests.cs
@@ -0,0 +1,114 @@
+using System;
+using System.Collections.Generic;
+using Shouldly;
+using Xunit;
+
+namespace AggregateConsistencyBoundary
+{
+    public class Tests
+    {
+        private readonly Shipment _shipment;
+
+        public Tests()
+        {
+            var stops = new List<Stop>
+            {
+                new PickupStop
+                {
+                    StopId = 1,
+                    Sequence = 1,
+                },
+                new DeliveryStop
+                {
+                    StopId = 2,
+                    Sequence = 2,
+                }
+            };
+            _shipment = new Shipment(stops);
+        }
+
+        [Fact]
+        public void CompleteShipment()
+        {
+            _shipment.Arrive(1);
+            _shipment.Pickup(1);
+            _shipment.Arrive(2);
+            _shipment.Deliver(2);
+            _shipment.IsComplete().ShouldBeTrue();
+        }
+
+        [Fact]
+        public void CannotPickupWithoutArriving()
+        {
+            Should.Throw<InvalidOperationException>(() => _shipment.Pickup(1), "Stop hasn't arrived yet.");
+        }
+
+        [Fact]
+        public void CannotDeliverWithoutArriving()
+        {
+            Should.Throw<InvalidOperationException>(() => _shipment.Deliver(2), "Stop hasn't arrived yet.");
+        }
+
+        [Fact]
+        public void CannotPickupAtDelivery()
+        {
+            Should.Throw<InvalidOperationException>(() => _shipment.Pickup(2), "Stop is not a delivery.");
+        }
+
+        [Fact]
+        public void CannotDeliverAtPickup()
+        {
+            Should.Throw<InvalidOperationException>(() => _shipment.Deliver(1), "Stop is not a pickup.");
+        }
+
+        [Fact]
+        public void ArriveStopDoesNotExist()
+        {
+            Should.Throw<InvalidOperationException>(() => _shipment.Arrive(0), "Stop does not exist.");
+        }
+
+        [Fact]
+        public void PickupStopDoesNotExist()
+        {
+            Should.Throw<InvalidOperationException>(() => _shipment.Pickup(0), "Stop does not exist.");
+        }
+
+        [Fact]
+        public void DeliverStopDoesNotExist()
+        {
+            Should.Throw<InvalidOperationException>(() => _shipment.Deliver(0), "Stop does not exist.");
+        }
+
+        [Fact]
+        public void ArriveNonDepartedStops()
+        {
+            _shipment.Arrive(1);
+            Should.Throw<InvalidOperationException>(() => _shipment.Arrive(2), "Previous stops have not departed.");
+        }
+
+        [Fact]
+        public void AlreadyArrived()
+        {
+            _shipment.Arrive(1);
+            Should.Throw<InvalidOperationException>(() => _shipment.Arrive(1), "Stop has already arrived.");
+        }
+
+        [Fact]
+        public void AlreadyPickedUp()
+        {
+            _shipment.Arrive(1);
+            _shipment.Pickup(1);
+            Should.Throw<InvalidOperationException>(() => _shipment.Pickup(1), "Stop has already departed.");
+        }
+
+        [Fact]
+        public void AlreadyDelivered()
+        {
+            _shipment.Arrive(1);
+            _shipment.Pickup(1);
+            _shipment.Arrive(2);
+            _shipment.Deliver(2);
+            Should.Throw<InvalidOperationException>(() => _shipment.Deliver(2), "Stop has already departed.");
+        }
+    }
+}
\ No newline at end of file