Десериализация сложного JSON объекта C#

Имеется сложный, не стандартный JSON объект:

{
    "id": "62",
    "contact_id": "1",
    "create_datetime": "2017-10-27 01:05:48",
    "update_datetime": null,
    "state_id": "new",
    "total": "332.2800",
    "currency": "RUB",
    "rate": "1.00000000",
    "tax": "0.0000",
    "shipping": "0.0000",
    "discount": "0.0000",
    "assigned_contact_id": null,
    "paid_year": null,
    "paid_quarter": null,
    "paid_month": null,
    "paid_date": null,
    "is_first": "0",
    "unsettled": "0",
    "comment": "",
    "params": {
        "ip": "194.186.172.92",
        "landing": "phimp.gif",
        "sales_channel": "",
        "shipping_address.country": "rus",
        "shipping_address.region": "72",
        "signup_url": "",
        "stock_id": "1",
        "storefront": "",
        "user_agent": "Mozilla\/5.0 (Windows NT 6.1; WOW64) AppleWebKit\/537.36 (KHTML, like Gecko) Chrome\/60.0.3112.113 YaBrowser\/17.9.1.768 Yowser\/2.5 Safari\/537.36"
    },
    "contact": {
        "id": "1",
        "name": "admin",
        "email": "1@1.ru",
        "phone": "79773013881",
        "registered": true,
        "photo_50x50": "Fuserpic50.jpg"
    },
    "items": {
        "84": {
            "id": "84",
            "order_id": "62",
            "name": "",
            "product_id": "171115",
            "sku_id": "218488",
            "sku_code": "516781",
            "type": "product",
            "service_id": null,
            "service_variant_id": null,
            "price": "110.7600",
            "quantity": "3",
            "parent_id": null,
            "stock_id": null,
            "virtualstock_id": null,
            "purchase_price": "0.0000",
            "total_discount": "0.0000",
            "image_id": "83660",
            "image_filename": "",
            "sku_image_id": null,
            "ext": "jpg",
            "file_name": "",
            "file_size": "0"
        }
    }
}

Описал классы:

    public class Order
    {
        public string id { get; set; }
        public string contact_id { get; set; }
        public string create_datetime { get; set; }
        public object update_datetime { get; set; }
        public string state_id { get; set; }
        public string total { get; set; }
        public string currency { get; set; }
        public string rate { get; set; }
        public string tax { get; set; }
        public string shipping { get; set; }
        public string discount { get; set; }
        public object assigned_contact_id { get; set; }
        public object paid_year { get; set; }
        public object paid_quarter { get; set; }
        public object paid_month { get; set; }
        public object paid_date { get; set; }
        public string is_first { get; set; }
        public string unsettled { get; set; }
        public string comment { get; set; }
        public Params _params { get; set; }
        public Contact contact { get; set; }
        public Items items { get; set; }
    }
    public class Params
    {
        public string ip { get; set; }
        public string landing { get; set; }
        public string sales_channel { get; set; }
        public string shipping_addresscountry { get; set; }
        public string shipping_addressregion { get; set; }
        public string signup_url { get; set; }
        public string stock_id { get; set; }
        public string storefront { get; set; }
        public string user_agent { get; set; }
    }
    public class Contact
    {
        public string id { get; set; }
        public string name { get; set; }
        public string email { get; set; }
        public string phone { get; set; }
        public bool registered { get; set; }
        public string photo_50x50 { get; set; }
    }
    public class Items
    {
        public Item[] item { get; set; }
    }
    public class Item
    {
        public string id { get; set; }
        public string order_id { get; set; }
        public string name { get; set; }
        public string product_id { get; set; }
        public string sku_id { get; set; }
        public string sku_code { get; set; }
        public string type { get; set; }
        public object service_id { get; set; }
        public object service_variant_id { get; set; }
        public string price { get; set; }
        public string quantity { get; set; }
        public object parent_id { get; set; }
        public object stock_id { get; set; }
        public object virtualstock_id { get; set; }
        public string purchase_price { get; set; }
        public string total_discount { get; set; }
        public string image_id { get; set; }
        public string image_filename { get; set; }
        public object sku_image_id { get; set; }
        public string ext { get; set; }
        public string file_name { get; set; }
        public string file_size { get; set; }
    }

Провожу десериализацию

var res = JsonConvert.DeserializeObject<Order>(str);

Ошибок не возникает, но возвращается null, т.е. Items = Null.

Грешу на то, что:

"items": {
    "84": {
        "id": "84",
        "order_id": "62",

Здесь что-то не так.

Как победить?