Getting derived object from the base object

No, I thought you understood the problem and was just verifying if you understood it correctly. Yes, I have a class public class MyTcpClient : TcpClient { public int ResourceIndex = -1; private NetworkStream ns; public delegate void TcpObjectHandler (TCPClient client, Infob iob); public event TcpObjectHandler ObjectArrived; public MyTcpClient() : base() {} public MyTcpClient(IPEndPoint localEP) : base(localEP) {} public MyTcpClient(AddressFamily family) : base(family) {} public MyTcpClient(string hostname, int port) : base(hostname, port) {} .... } Now, I set up a TcpListener object that has a method AcceptTcpClient() which returns a TcpClient object. I need to take that object and get an instance of MyTcpClient. Doing this: TcpListener listener = new TcpListener(IPAddress.Any, port); listener.Start(); while(true) { Thread.Sleep(1000); if(!listener.Pending()) continue; MyTcpClient newClient = (MyTcpClient)listener.AcceptTcpClient(); ... } fails during runtime - invalid cast exception. I expected this because the TcpClient object that AcceptTcpClient() returned wasn't boxed from MyTcpClient originally, so the cast fails. My next attempt was to add another constructor to MyTcpClient that took an instance of TcpClient and tried to assign it to base, like so: public MyTcpClient (TcpClient client) { base = client; } which failed to compile - cannot use the base keyword in that context. So, my problem/question is - how do I get an instance of a derived object from an instance of the base object?