Julian Barnes' gay detective

At last week's meeting, Ernie Raskauskas mentioned that under the pen name Dan Kavanagh, Julian Barnes wrote a series of four novels featuring Nick Duffy, a bisexual ex-cop turned security consultant. Octavio Roca has also read The Duffy Omnibus and was kind enough to share a photo of the cover. The books are out of print, alas, but are available from used-book dealers.