diff --git a/simple_message_channels/smc.py b/simple_message_channels/smc.py
index 1063e2b..89f90c0 100644
--- a/simple_message_channels/smc.py
+++ b/simple_message_channels/smc.py
@@ -11,6 +11,7 @@ __all__ = ["SimpleMessageChannel"]
 class SimpleMessageChannel:
     """A simple message channel."""
 
+    message: bytes = attr.Factory(bytes)
     messages: List[Tuple[int, int, bytes]] = attr.Factory(list)
 
     varint: int = 0
@@ -60,7 +61,22 @@ class SimpleMessageChannel:
 
     def _read_msg(self, data: bytes, offset: int) -> int:
         """TODO."""
-        pass
+        free = len(data) - offset
+
+        if free >= self.length:
+            if self.message:
+                self.message += data
+            else:
+                self.message = data[offset : offset + self.length]
+
+            offset += self.length
+            self._next_state(data, offset)
+            return offset
+
+        self.message += data
+        self.length -= free
+
+        return len(data)
 
     def _read_varint(self, data: bytes, offset: int) -> int:
         """TODO."""
@@ -69,10 +85,8 @@ class SimpleMessageChannel:
             self.consumed += 1
 
             if data[offset] < 128:
-                state = self._next_state(data, offset + 1)
-                if state:
-                    return offset
-                return len(data)
+                self._next_state(data, offset + 1)
+                return offset
 
             offset += 1
 
@@ -83,4 +97,23 @@ class SimpleMessageChannel:
 
     def _next_state(self, data: bytes, offset: int) -> bool:
         """TODO."""
-        pass
+        if self.state == 0:
+            self.state = 1
+            self.factor = 1
+            self.length = self.varint
+            self.consumed = 0
+            self.varint = 0
+            if not self.length:
+                self.varint = 0
+        elif self.state == 1:
+            self.state = 2
+            self.factor = 1
+            self.header = self.varint
+            self.length -= self.consumed
+            self.consumed = 0
+            self.varint = 0
+            if self.length < 0 or self.length > self.max_size:
+                raise RuntimeError("Incoming message too large")
+        else:
+            self.state = 0
+            self.message = b""