Can any one tell me how to concate two lines for the following case

I have a file where continuation for one line is printed in the next line starting with a '+' sign. so i want to concat the two lines with out the + sign

eg:

Hello how are you?
+ you didn't come yesterday
Are you there
I guess you are here...

output for the above case should be:


Hello how are you? you didn't come yesterday
Are you there
I guess you are here...

Thanks in advance
-Ranjith