Wilkie Collins visited the United States from September 1873 until March 1874. To mark the occasion, Harper & Brothers issued a collected edition of his works, beginning with The New Magdalen on 8 November. The Dead Secret was published just before Christmas, the fifth in the series. 
The verso of the title page showing 11 volumes priced at $1.50. As well as the signature on the front cover, each volume contained this printed dedication.
The first issue of Harper's Library Edition have the date on the title page. Later they were re-issued at $1.25 with no date on the title page, though there could be a date of 1873 on the verso of it. Some contain adverts at the end. 

All material on these pages is Paul Lewis 1997-2000