void Main()
{
    var groups_to_querry = new List<Groups>();
    var contacts = groups_to_querry
                .SelectMany(x => x.Contacts)
                .Where(x => x.ID == Guid.Empty)
                .SelectMany(p => p.ContactDetails)
                .Where(x => x.ID == Guid.Empty)
                .SelectMany(x => x.Contacts);
}

class Groups
{
    public ICollection<Contact> Contacts { get; set; }
}
class Contact
{
    public Guid ID { get; set; }
    public ICollection<ContactDetail> ContactDetails { get; set; }
}
class ContactDetail
{
    public Guid ID { get; set; }
    public ICollection<Contact> Contacts { get; set; }
}