Bus from Trpanj to Dubrovnik

[Mark]

 I plan to arrive in Trpanj the 1415 ferry from Ploce (arr Trpanj around 1510) on 28 Oct and I am wondering if I must return to Ploce to find transportation to Dubrovnik or whether there is some way to make my way on land with a bus either directly to Dubrovnik or to some other town on Peljesac (Ston?) from where I can catch a bus to Dubrovnik. 

According to  published schedule, there aren't any busses leaving Trpanj in the afternoon. 

Any information you can supply would be greatly appreciated. 

Many thanks.  Mark.