C#: Create an Expression to use with LINQ

gistfile1.cs

 public ActionResult Grid(string FirstName, string LastName)
        {
            GridHelper.Filters filter = new GridHelper.Filters("FirstName", "LastName");

            var _page =(!String.IsNullOrEmpty(HttpContext.Request.QueryString["page"])) ?  Convert.ToInt32(HttpContext.Request.QueryString["page"]) : 1;
            var _contacts = from c in testDB.Contacts
                             join ac in testDB.Account_Contact on c.ID equals ac.ContactID
                             where ac.AccountID == 725
                             select c;


            // Create the parameter (typically the 'x' in your expression (x => 'x')
            ParameterExpression param = Expression.Parameter(typeof(Contact), "parm");

            // Store the result of a calculated Expression
            Expression exp = null;

            if (!String.IsNullOrEmpty(filter.List["FirstName"]))
            {
                // The member you want to evaluate (x => x.FirstName)
                MemberExpression member = Expression.Property(param, "FirstName");

                // The method you want to use to create an 'IN' statement
                MethodInfo method = typeof(string).GetMethod("Contains", new[] { typeof(string) });

                // The value you want to evaluate
                ConstantExpression constant = Expression.Constant(filter.List["FirstName"]);
                //BinaryExpression result = Expression.Equal(member, constant);

                // Actually apply the expression together (x => x.FirstName.Contains('value'))
                MethodCallExpression result = Expression.Call(member, method, constant);

                // The Result
                exp = result;

                // Creates the expression against the type
                Expression<Func<Contact, bool>> deleg = Expression.Lambda<Func<Contact, bool>>(exp, param);

                // Apply our newly created expression against the .Where clause
                _contacts = _contacts.Where(deleg);
            }


            ViewBag.Data = _contacts.ToList();
            return View();
        }