Maessen's second pop single, "Knock, Knock Who's There?" was a cover version of Mary Hopkin's entry in the Eurovision Song Contest 1970. It was released on Fable Records in April 1970 and peaked at No. 2. It co-charted with Hopkin's version. During the 1970 radio ban, a major dispute between commercial radio stations and record companies, Hopkin's version was not well known to Australian listeners. "Knock, Knock Who's There?" finished third on "Go-Set"s Top Records for the Year of 1970 and was the highest placed by an Australian artist. Maessen became the first Australian female artist to be awarded a gold record certificate for a single with sales of over 50,000. She won the 1970 Logie Award for "Best New Talent" and in the "Go-Set" Pop Poll was voted in the top five as most popular female vocalist.