Supreme Court Act 1979

The Court has power to grant to a defendant, in respect of an equitable estate or right or other matter of equity, and also in respect of a legal estate, right or title claimed or asserted by him:

all such relief against a plaintiff as the defendant has properly claimed by his pleading and as the Court might have granted in a proceeding instituted for that purpose by that defendant against the same plaintiff; and

all such relief relating to or connected with the original subject of the proceeding, being relief claimed in like manner against another person, whether already a party to the proceeding or not, who has been duly served with notice in writing of the claim pursuant to the Rules, any other law in force in the Territory, or an order of the Court, as might properly have been granted against that person if he had been made a defendant to a proceeding duly instituted by the same defendant for the like purpose.

A person served with such a notice shall thenceforth be deemed a party to the proceeding with the same rights in respect of his defence against the claim as if he had been duly sued in the ordinary way by the defendant.