public void TradeSpell(Spell s, Investigator previousOwner)
    {
        Investigator i1 = App.Model.tradeModel.investigator1;
        Investigator i2 = App.Model.tradeModel.investigator2;

        if (previousOwner.investigatorName == i1.investigatorName)
        {
            // i2 gains spell
            i1.TradeSpell(s, false);
            i2.TradeSpell(s, true);
        }
        else
        {
            // i1 gains spell
            i2.TradeSpell(s, false);
            i1.TradeSpell(s, true);
        }
        App.View.tradeView.TradeMade();
    }