A person who is not a party to an action may only be brought in under the third party procedure if the defendant claims to be entitled to contribution
from or indemnity against him. The defendant has a claim to such indemnity which would justify bringing in the third party, if the plaintiff's action against him succeeded and did not at the same time
defeat the claim against the third party

\Vhere a vendor contracts to sell property to a purchaser and later purports to sell the
same property to a third party who takes with full notice of the prior contract, the third party's rights are subordinated to those of the purchaser. There is in any event, implied in the first contract of sale, an obligation on the part of the vendor to indemnify the purchaser against subsequent dealing with the property to his detriment