The novel takes place on the Isle of Wight. The Isle of Wight is a county and the largest and second-most populous island in England. It is in the English Channel, about 6 km off the coast of Hampshire, separated by the Solent.
One of the towns is Newport, which I think is where Emily and her family live. The town is situated slightly to the north of the centre of the Island.
There are many references to different places on the island. For example, when Emily and Marcus have sex, they go to Shanklin Beach, which is the one of the best-known beaches on the island.
Avril arranges to meet James in Ventnor Botanic Garden.
After Avril realises that James is not trustworthy, she goes to Lymmington Harbour by ferry. Lymington is a port town on the west bank of the Lymington River on the Solent, in the New Forest district of Hampshire.
Alum Bay is close to the Needles, and it is there that Emily hears the body of a baby has been found. Alum Bay is a bay near the westernmost point of the Isle of Wight, within close sight of the Needles rock formation. Of geological interest and a tourist attraction, the bay is noted for its multi-coloured sand cliffs.