ACROSS
 1. (.v)IDEO LOG I ES(p.) = IDELOGOIES <principled beliefs>
 6. "LOO DOUGH" = LUDO <dice game>
10. <interrupt> CUT IN = CU + TIN
11. CULTIVAR* E = LUCRATIVE <profitable>
12. S_ + PACES HIP = SPACESHIP <vehicle>
13. <betray> RAT ON = R (A TON)
14. <praised> LAUDED = "LAW DID"
16. <raise your weapon> EN GARDE = GRENADE*
18. AENEID'S* = ANISEED <word for a spice>
20. PAN + TRY = PANTRY <larder>
22. S inside (TO A T) = TOAST <cooked bread>
23. <lawyer> BARRISTER = BARRIER outside _S _T
25. <no hope for this> LOST CAUSE = CASSOULET*
26. _E _L after LAB = LABEL <tag>
27. "MAC C" = MAXI <ankle-length>
28. <most mysterious> SHADOWIEST = (AT SIDESHOW)*

DOWN
 1. "INN SIZE" = INCISE <cut>
 2. <part of open relationship> EXTRAMARITAL SEX = (MARTIAL ARTS)* inside (EX EX)
 3. LUNG + E_ = LUNGE <leg exercise>
 4. GALA HAD = GALAHD <knight>
 5. "S_ K_ P_" = ESCAPEE <fugitive>
 7. PRINTER* inside UNE + TABLE = UNINTERPRETABLE <impossible to decipher>
 8. <evergreen> OLEANDER = O + LEANDER
 9. <perennial> TARRAGON = TAR + (RAG ON)
15. <thread-cutting tool> DIESTOCK = ←(.n)K COT'S EID(e.)←
17. TAN TALCUM - C = TANTALUM <another element>
19. <seduce> DEBAUCH = DEB + AU + C_H
20. (PER SE) I'D = PERSEID <shooting star>
21. METAL* outside _R = ARMLET <band>
24. _I_N_L_A_ W_ = IN-LAW <family member>