In " Avenging Angel " ( 1993 ) , MacLeod and Tessa search for information about newborn Immortal Alfred Cahill ( Martin Kemp ) . Becoming Immortal have made Cahill insane ; he believe he is an angel sent by God to free the world from sin . Cahill start with the last prostitute he met , Tessa 's old friend , Elaine Trent ( Sandra Nelson ) . Tessa is angry to learn the fate of her intelligent , beautiful friend , but later realize that she " [ sound ] like her judge and jury . " MacLeod believe that the only way to stop Cahill is to behead him , despite Tessa 's opinion that " Enlightened societies don 't kill their insane . They treat them . " When Cahill come to the barge looking for MacLeod and find Tessa alone , Tessa divert him by welcoming Cahill as a messenger of God . Later , she tell MacLeod with disgust , " I had to crawl inside his head ... I had to think like him ... I had to become like him . "