Part of Mollie's plan: a delightful walk by the seaside? (9)
I believe the answer is:
esplanade
'walk by the seaside?' is the definition.
(area for walking by the sea)
'part of mollie's plan a delightful' is the wordplay.
'part of' indicates a hidden word.
'ESPLANADE' can be found hidden inside 'mollies plan a delightful'.
(Other definitions for esplanade that I've seen before include "Level seashore walkway" , "Seafront walkway" , "Promenade" , "Seaside resort walk" , "Walkway beside the seashore" .)